Are you talking about pitting in the bore of the barrel or on the outside?
Either way, you are not going to be able to remove them. The pits are metal that has been disolved, probably from rust. You can't put the metal back and if it's in the bore, you do not want to remove any more metal than is already gone or you'll end up with a smoothbore.
If it's on the outside, I guess you may be able to have somebody remove the barrel and turn it down on a lathe to remove the rusted layer, but it's probably not worth the expense.
The best you can do is damage control: Use some Breakfree CLP or KROIL and a brass brush to remove any active rust, then reblue the area with Cold Blue (I like the Brownell's Gel). On some guns, a dark Parkerizing or using something like Flat Black Gunkote may make the damaged area less obvious.
If the pits are very deep, the rifle may be unsafe to fire. Can you take any pics of the damaged area?