IPHONE ON TESTFLIGHT

Trying 2 download an app called ZiniTevi but it says install Testflight also says join beta But iv never ad download test bfor to get app i want i only ad to delete it due to ios update needed memory thats when i cudt get it back , i clicked on join testflight but says cant Anybody get wot my problam is am aving i need it all this iphone technoligy is still very new im not that knowlageable yet

used on iphone 7 also 6s