Have you checked the switch inside the glove box?

 

I'm having the same rear lift gate problem with my 2017 Murano SL. Would not open electronically or manually. Took it into the dealer and they "reprogrammed it". Three days later it is not working again. Taking it back in again this Wednesday. What a pain!

 

If you need to open it manually you can insert a screwdriver in the lower part of the small grille from the inside to release the lock (check your manual).

 

Same with me. You can try reseating the fuse in the engin bay (its the 40-40-40 amp block). It?ll work but problem will resurface. Mine is at the shop now.