Screen Time forgotten passcode

About the Screen Time passcode on managed devices - Apple Support

Screen Time passcode reset

Forgotten Restrictions Passcode Help

  •   iPad,iPod,iPod Touch Recovery Mode

  •   How to erase your iOS device & then set it up as a new device or restore it from backups

  •   About Restrictions (parental controls) on iPhone, iPad, and iPod touch - Apple Support

  •   Use parental controls on your iPhone, iPad, and iPod touch - Apple Support

You will need to restore your device as New to remove a Restrictions passcode. Go through the normal process to restore your device, but when you see the options to restore as New or from a backup, be sure to choose New. You can restore from a backup only if you have one from BEFORE you set the restrictions passcode.

If using IOS 13.4 or newer.

Screen Time passcode reset

Another option.

You will need to restore the device to factory settings. Do not restore from a backup made when the Screen Time code was active.

Restore to Factory setting.      

Backup - Restore your device from an iCloud or iTunes backup.