forget my screen time code

From the article below.

To change or turn off the passcode on your child's device, tap Settings > Screen Time > [your child's name]. Then tap Change Screen Time Passcode or Turn Off Screen Time Passcode, and authenticate the change with Face ID, Touch ID, or your device passcode.

Parental controls

If that doesn't work, 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