How can I find screentime password on ios12?

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 or later, you should update to the most current version before attempting to resolve a forgotten ScreenTime passcode. The most recent iPadOS updates have introduced a 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.

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

If you've forgotten your Screen Time passcode, update your device to the latest iOS or iPadOS, then reset your passcode. Apple added the “Forgot Passcode” button in iPadOS 13.4.

Can you provide your iPad’s model number? iPad mini 4 and later can run iPadOS 15.

If the software version is iOS 12.4.1 or earlier, it may be iPad mini 2, 3, 4 or 5.

If the software version is iOS 12.4.2 or later, assuming it is iOS 12.x, it is probably iPad mini 2 or 3.

As you are unable to reset the ScreenTime Passcode without a full reset, if you have any data or documents that must be preserved, your priority must be to manually copy/backup this data to external media - or other Cloud service.

After creating an independent backup of your data, you can then fully reset your iPad - and set-up again as new. After the reset, you can copy your data back to your iPad.

A reset of your iPad is perhaps not as devastating as might be first thought - as any data (e.g., Calendar, Contacts, Reminders, Notes, Keychain etc.), Photos and documents natively synchronised with iCloud will not be lost. These will be synchronised back to your iPad after signing-in with your AppleID. Likewise, your email messages will also remain on your email providers Mail server - and will similarly be copied back to your iPad when you re-add your Mail account(s).