I am getting this as a reminder every 1 hr, do i really have to install such an app ?

If running iOS 13, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

Don’t install anything. It’s a scam.

You’re welcome.