Has the transmission completely failed, and the car is no longer drivable?
If yes, you are already too late.
If the car is just starting to slip, then here's what you can try to do:
Go buy the Nissan fluid, enough for 2 full transmission fluid changes.
Have it changed, and if the car can drive, drive it for a week, and then change it again, and drive it for another week.
If it still is causing you trouble, then take it to a DIFFERENT Nissan dealer, and tell them you are having issues with it.
Yes, for Nissan's CVT transmissions, you MUST ONLY use the Nissan Fluid.
I wouldn't even trust the Valvoline stuff that says it's compatible, unless you can get a letter from Valvoline stating that they are Nissan's CVT fluid supplier.