I wanted to update my explanation ^ a little bit - it's based on how trim works in smaller trainer aircraft (which are all I've flown). On a 737 there isn't a "trim tab" - instead the whole littler wing at the back of the airplane (tailplane) can change its position based on the trim, while the elevator is the adjustable tab at the back of that which moves based on the pilot's inputs.

I think the basic procedure for how to undo the excessive trim based on too much force to move the tailplane still is accurate though...

I just read this great article (https://www.skybrary.aero/bookshelf/books/2627.pdf) linked lower down in this thread for more details.