App from iCloud backup , no access to gallery

I’ve just purchased an iPhone 6s , I engaged iCloud backup and successfully changed all my relevant detail from my old iPhone6 Unfortunately the app featured would not give me access to my photo/ videos I just got this , I went into Privacy settings and because it hadn’t asked me for access to my gallery would not transport. Rendering the app useless , as I can’t gain access to import or export any of my files I tried to delete and reinstall through iCloud but it said I would lose all data , Any help would be appreciated