how torecover screen time passcode?

From the article below.

If you can't remember a restrictions passcode that you created on a previous version of iOS, or you forgot your Screen

Time passcode, you need to erase your device, then set it up as new to remove the passcode. Restoring your device won't remove your old passcode.

Parental controls. https://support.apple.com/en-us/HT201304

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. https://support.apple.com/en-us/HT201252

This discussion (What is Screen Time passcode in iOS 12?) from here may be useful to you. I am not sure. https://discussions.apple.com/thread/8539968