Minimum requirements to remove that pascode:
- Device running iOS 13.4 or later
- Knowledge of the Apple ID & Password that were used to set up your ScreenTime passcode.
If you meet both of those requirements, perform this procedure:--> If you forgot your Screen Time passcode – Apple Support
If you do not meet the above requirements, you won't be able to reset/change it and you need to erase your device's content using this procedure (even if not related to the ScreenTime passcode):--> If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support
The bad news is that your cannot restore data from a backup, since the ScreenTime passcode would come back.
Regards
Giulio