They will do it by outlawing certain things, and then giving people a short time to adjust by giving up rights to those arms and switching to what is still legal. They will add new paperwork, restrictions and tracking, then wait until it just seems normal.
If you look around the world they have not just stormed in to each and every place with paramilitary "swat" teams. That is a tactic reserved for a limited percent.
When hunters and shooters have one type banned, history shows us they bellyache and moan, a couple need tactical responses, but most willingly give up the outlawed type and then do whatever new ridiculous process is required to retain thier ability to use what is still legal. Since some things are still legal, it is never and "all or nothing" situation that would cause the people to resist or revolt.
We see this in Australia where they lost many of thier rights suddenly, and ownership turned into a several month long process for limited types of firearms for those determined individuals.
We see it in the U.K. where handguns were banned, and semi auto rifles and most repeating firearms have been banned for ownership by the general public.
We see it with the assault weapon ban when all of America was suddenly forbidden from various additions on firearms and normal capacity.
They pacify the reaction by saying "It is all illegal, except this _____, but to own _____ is no longer a right, but a privelidge you need to fill out tons of paperwork, and be given permission to own. The owner says "oh, well that is not so much different than before" because they have progressively been introduced to such a process prior to various bans already.
Take America. 100 years ago the average person would consider what we have now no different than how we view the U.K. Firearms are not banned, but many types are restricted or prohibited, and infringement is all around requiring various processes. Various types of people can and are routinely banned from ownership, something unheard of for any free man. Forms are kept about purchases, permission is required through a NICs system etc
If you brought thousands of Americans from the past through time to the future they would think we live in an unfree police state and probably rebel and require a military response. However we have been conditioned. If they outlaw assault weapons, we buy something else. If they outlaw various types of weapons or features, we comply and stay within limitations. If they outlaw a new type, we comply and own what is left. If invasive procedures become required to qualify for ownership, we go through those procedures.
Of course each and every step causes less people to actualy go through with purchasing or becoming new firearm owners. So ownership overall slowly shrinks, and hunters and shooters become fewer and fewer, and willing to tolerate more and more restrictions, and complete more and more forms to continue ownership and use of thier firearms. Eventualy all the have is over-under sxs and single shots, and can only use them in very limited circumstances, paying various fees, and must store them taken apart and locked away.
As all of this changes, people begin to become more passive, and view tools used for self reliance not just limited to firearms or weapons, but everything in general as bad. Licenses become required for everything, to build anything, to create anything, etc. It becomes a society where only the "professionals" can use various tools. Defense becomes delegated to such professionals.
So people imagining suddenly everything will be banned overnight, and all hope will be taken away from the herd is naive. If you take Tyrant 101 you would know that as an effective tyrant you never remove hope, because then the population starts to resist. Hope is what makes cattle march up to the slaughter house believing the people that helped them be born and brought into the world, fed them, took care of them, and provide for thier various needs are to be trusted. Even though they can smell blood, know it is probably a bad idea, they march on.
Even the Nazis understood this. They didn't just round up people to kill them, that would have resulted in revolution and organized resistance when it could be effective, thier enemies still had positions of power, and were well connected. They progressively removed rights, ownership of items which could be used against them, etc.
They made the people they captured believe they could behave a certain way and things would work out for them. They didn't remove hope. They made them think they just wanted to work them as a free labor force. It took a few years after they finaly had the Jews and others right where they wanted them, weak from malnutrition, used to following orders etc before they started doing the things they are famous for now on a wide scale.
The same goes for most Kings throughout history. Removing hope from your subjects is something you never do unless you become desperate.
You always make them feel they can adjust and work with the solutions you provide. Not that all is lost.
So to imagine that armed paramilatary units will go door to door removing ownership is naive. The manpower necessary for that limits it to the small number who resist, or openly defy. They will just gradualy ban more things, make ownership more difficult, and put things in place to know who has what so they can selectively target those that don't comply with new progressive bans.
In fact if you consider that the 2nd was created to give people the ability to own things on par with the infantry used by tyranny, so they could organize into militias and resist them... Then we have already lost. What would be necessary to resist our armed forces effectively has already been outlawed. To mount an effective resistance people would already have to create illegal things. So the intent of the 2nd failed long ago. It is only symbolic now.