The 629 is a stainless .44 revolver, so I'm guessing you meant 639. I'm not personally familiar with the tear-down for that model so I'll suggest you do what I do in these cases- beat the internet to death for schematics, disassembly instructions etc. Then again, someone may be along shortly who knows exactly how to go about it.
“Nine-tenths of tactics are certain, and taught in books: but the irrational tenth is like the kingfisher flashing across the pool, and that is the test of generals. It can only be ensured by instinct, sharpened by thought practicing the stroke so often that at the crisis it is as natural as a reflex.” ~ T. E. Lawrence