How to reset screen time pass code on my iPad mini 3

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

To reset a forgotten ScreenTime passcode on versions of iOS/iPadOS preceding iPadOS13, the iPad must be reset “as new”, losing all locally stored data. You’ll not be able to restore your data from an iCloud or iTunes backup - as the forgotten passcode is integral to the backup.

I hope this information is helpful to you in successfully resetting your forgotten passcode.