Application

Did you possibly download it on another iCloud device? Sometimes downloading an app on another device will install it on your other iCloud devices. If you didn't, just delete the app (it shouldn't be malicious if it was approved on the App Store).

Ok, that’s a good idea. In case they didn’t give you the Support links for backing up, and restoring, I’ll link them below. Best of luck! - Owen

Back up iPhone

Restore your iPhone to factory settings

Restore your iPhone from an backup