How can I use openstore(apps) in Fairphone Open (Fairphone 2)?

First I tried hard to use UT on Fairphone 2, but so far the camera flash (LED) does not work. :-((( To be able to use the camera flash of the fairphone, I switched to the OS "fairphone open".

Before I liked the "TankenAPP" (gasoline price in Germany) from the openstore. The f-droid store does not offer an app for German gasoline prices.

I would like to use the "TankenAPP" from the openstore. I just noticed that a *.click file is displayed when downloading (com.ubuntu.developer.derjasper.tankenapp_0.4.15_all.click).

?: (How) can I install this on the OS fairphone?

Precautionary I ask for your indulgence that I still have very little experience.

Dear Community,
I´m new in this forum and hope I start in the right way.

I have bought a used
Fairphone 2
OS Umbuntu touch
12MP, doublelight flash

With this phone the flash does not work (camera itself works fine), neither when taking pictures (flash [on] or [automatically] ) nor with a flashlight app (uTorch).
I have already removed the camera module, cleaned the contacts and reinstalled it. I´ve bought a spare camera modul that showed no (better) effect.
The OS update to Ubuntu 16.04 (OTA-14) did´nt help.

P.S.:
I take over trucks at night and have to take pictures of damages before. Without a working flash my smartphone is no help then.

I look forward to your suggestion with great interest.