To reset or change your iPad's passcode, you can use the "Passcode" menu in your Settings app, or reset the entire device.
Recovery Mode: Connect iPad to a computer > open Finder (Catalina or later) or iTunes > restart > Update from the recovery screen. If you don't have access to a computer, use iCloud to wipe the iPad ...
Before you lock your iPad, you should set up a security method. Depending on your iPad model, this can include Touch ID or ...