How to reset screen time password.

To reset the Screen Time passcode, follow the steps in this article:

If you forgot your Screen Time passcode - Apple Support

But, if your iPad is not able to update to a newer version than iOS 12, you will need to erase the iPad and set it up as a new device, without using the latest backup. The Screen Time code is part of the backup data and will be reinstalled if you restore from that backup.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

If you have forgotten the ScreenTime passcode, one of the two procedures outlined within this link should resolve the problem:

If you forgot your Screen Time passcode - Apple Support

If your iPad is capable of supporting iPadOS 13.x, you should update to the most current version before attempting to resolve a forgotten ScreenTime passcode. The most recent iPadOS updates have introduced a new mechanism whereby a forgotten ScreenTime passcode can be reset without wiping the iPad.

To reset a forgotten ScreenTime passcode on older versions of iOS/iPadOS, the iPad must be reset “as new”, losing all locally stored data. In this situation, you’ll not be able to restore your data from an iCloud or iTunes backup - as the forgotten passcode is integral to the backup.