push button trans won't go into reverse.

#1 did this work before?
#2 have you lubed any part of the cable ,shifter mechanism?
#3 have you properly adjusted the cable?

I would start by inspecting & seeing if anything is broken or missing ,etc.., if not lube the cable & the mechanism & then adjust it correctly by Fsm procedure.

then if it doesn't work start diagnosing.

Lawrence