Those seat backs are buggers and there are no real short cuts if the cable is broken. If you do need to disassemble the seat back, have a handful of the white clips for the seatback board on hand, they
always break. P/n for those is 88746-6FU0A.
Most of the time the problem will be a broken lever and not a broken cable, and you can usually fish the cable out and replace the lever without disassembling the seat back. That isn't difficult, but for some reason the "dissassembly" section in the FSM doesn't tell you there's only one screw holding the lever and escutcheon to the frame. It's hiding under the lever and you can see it in the exploded drawing if you look close. See SE-64 here, it's the un-numbered fastener shown with item #33:
https://www.nicoclub.com/service-manual ... 6%2FSE.pdf
If the lever is broken, then the cable-end may be deep down in the hole. If so, you'll need a good fishing tool like a long hemostat to get it out. Magnets don't work, the pivot ends on the cables are white-metal.