Here is Apple’s guidance on changing/removing/reseting the ScreeTime passcode.
https://support.apple.com/en-us/HT211021
If you are currently running and version of iPadOS prior to iPadOS 13.4.1, update to this version if you can. Once updated to iPadOS 13.4.1, a mechanism exists to reset the ScreenTime passcode.
If you cannot update to iPadOS 13.4.1, or you have an earlier version of iOS installed, it is not possible to reset a forgotten ScreeTime passcode. Instead, you must erase and set-up again as new - and will not be able to restore data from you backup (the backup will contain the encrypted ScreenTime passcode that has been forgotten).
I hope this clarification is helpful.