There is no return to the gym program for a reason: You don’t need any special training or anything like that.
Train the same way (more or less… maybe dial back the intensity/volume by feel) you built up your strength/muscle the first time around tho you’ll it’ll be easier/faster this time around. Might be awkward at first as your technique comes back to you but muscle and strength will soon follow.
Muscle memory:
If you’ve done cycles before permanent physiological change to muscle persisting after cessation of use:
If you want to try something different in returning to training you’ll still get the boost from the above factors. Maybe a hybrid kinda program midway between bodybuilding and strength/powerlifting could work well for you e.g. Juggernaut 2.0