You will have to take off the left side plate, FIRST -
use a paper clip to pin the hole at the end of the Hammer Strut.
Release the hammer by holding the hammer and pressing on the trigger. THis will press the strut spring on the paper clip and hold the spring on the strut.
remove the Hammer pivot pin retaining ring (snap ring) then the left side plate
remove the strut spring/strut/strut bridge assembly (held in place by the paper clip)
Remove the return spring pin (#67) replace the hammer return spring- reinsert pin - remember that the spring goes on top of the trigger end piece.
attach the strut spring while putting the left side place back in place.
install the Hammer pivot pin retaining ring (snap ring that holds the left side plate in place).
Pull the hammer back until it locks.
remove the paper clip..