You fix it by
not doing any of what you have attempted... Do a search on the forum for "Play Store". Results will show MANY threads on this subject.
The controllers for the majority of Yuneec products have a
limited version of Android to provide a basic OS for the flight firmware.
PLAY STORE IS NOT SUPPOSED TO "WORK" on your controller.
Regarding your issues with UAV Toolbox, your questions should be addressed to the developer,
@Tuna.
No apps from PlayStore should attempted to be loaded. That is what your phone or tablet is for. The controller is only dedicated to flying your aircraft. If you want a setup that allows all sorts of extra apps (including the one to operate your drone), I suggest DJI... they have several choices.