(> iOS15.2) See this Apple article: If you've forgotten your iPad passcode
If you’ve forgotten your iPad passcode – Apple Support (UK)
(iOS 15.2 and newer) How to reset your iPhone, iPad or iPod touch if you've forgotten your passcode
How to reset your iPhone, iPad or iPod touch if you've forgotten your passcode – Apple Support (UK)
Check your Apple ID via your email box, see this Apple article: If you forgot your Apple ID
If you forgot your Apple ID email address or phone number - Apple Support
OR see -> Having trouble signing in?
https://iforgot.apple.com/password/verify/appleid
If you've forgotten your Apple ID email address or phone number
If you've forgotten your Apple ID email address or phone number – Apple Support (UK)
See this Apple article: If you forgot your Apple ID password
If you forgot your Apple ID password - Apple Support
Then see this Apple article: What to do after you change your Apple ID or password
What to do after you change your Apple ID or password - Apple Support