To put a John Deere deck belt riding mower back on track, pull the left foot plate up then proceed to disengage the hinge tabs. Doing so eventually releases the foot plates.
Another way to put the mower back on track is to remove the belt shield locking rings. Then, lift the corner of the belt shield from the drilled stud. Also, try getting a wrench to replace the overly stretched or broken one, or try fitting the proper-sized wrench on the three pins that are screwed into the frame under the engine and next to the pulley under the engine itself.