Use these steps to reset it and regain access to your account.
If you've forgotten your iPad passcode – Apple Support (UK)
Help a friend or family member as their account recovery contact - Apple Support
If you forgot your iPad passcode, use your Mac or PC to reset it - Apple Support (CA)
If you forgot your Apple ID password Iphone features, Apple support, Password security
If you forgot your Apple ID password - Apple Support (CA)
How to Reset Your Apple ID Password in a Few Easy Steps
If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support
What If You Forgot Your Apple Id Password - SADA Tech
How To Reset Your Apple ID Password by Email - GadgetMates
Add or remove your phone number in Messages or FaceTime - Apple Support (CA)