Hi I have virus on my iPad

You installed calendar spam that is lying to you about having a virus. Ignore all such nonsense and remove the calendar in Settings.

Remove spam from Calendar on your iPhone - Apple Support

If running iOS 13 or earlier, 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.