WARNING: resetting deletes all files inside the iPad. Back up your files before doing so.

1. Have a PC with iTunes or a Mac ready, along with a lightning cable.

2. Bring your iPad to recovery mode by holding the lock and home button together till you see the 'recovery mode' screen.

3. Connect the iPad to your pc/mac.

4. The iPad will be automatically detected, and a prompt will appear.

5. Choose, 'Restore'.

6. When it completes, go through the initial setup (Please do not sign in or load from a backup).

source: https://support.apple.com/en-us/HT212787