To remove the Model 39 firing pin:
First, if the ambi safety is installed, remove the right hand thumbpiece. Then with a small punch, push the firing pin in past the safety. Holding it there*, move the safety to a position halfway between on and off and push the safety out from the right side, releasing pressure on the firing pin when the safety moves enough to block it. Make sure not to lose any small parts.
Reinstall by inserting the firing pin and spring, pushing them down while the safety is inserted. Reinstall the right hand thumbpiece if applicable. You will have to press in the safety plunger to get the safety back in.
*You can hold the front of the firing pin with small lock pliers, but that is not really necessary.
HTH
Jim