What if I forget the lock screen password of a Sub user or Guest mode

Sub users:

The password cannot be retrieved, and you can restart the phone and return to the Owner system. 

Go to Settings > Users & accounts > Multiple users > Sub-User system settings > Delete User (Sub-user data will be cleared), and then create a new sub-user.

Guests: 

The password cannot be retrieved, you can restart the phone and return to the Owner system.

Go to Settings > Users & accounts > Multiple Users > Click on Guest > Restart (Previous guest data will be cleared).