If you know the passcode, go to Settings > General > Transfer or Reset iPad > Erase All Content and Settings
If you forgot the passcode, put the iPad in recovery mode
Connect the iPad to a Mac or PC with a USB cable
Open Finder on Mac with macOS Catalina or later
Open iTunes or Apple Devices on Windows or older macOS
Force restart the iPad and keep holding until the recovery mode screen appears
When prompted, choose Restore
Wait for the computer to download and reinstall iPadOS
If the download takes too long and the iPad exits recovery mode, repeat the recovery mode steps
If Find My iPad is enabled, erase the device using iCloud.com/find or the Find My app
Sign in with the Apple ID and password after reset if Activation Lock appears
If you cannot access the Apple ID, contact Apple Support with proof of purchase