Activation lock

See this Apple article: How to remove Activation Lock

https://support.apple.com/en-us/HT201441

Have you forgotten your Apple ID?, check your Apple ID via your email box, see this Apple article: If you forgot your Apple ID

https://support.apple.com/en-us/HT201354                  

OR see -> Having trouble signing in?

https://iforgot.apple.com/password/verify/appleid

Have you forgotten your password? -> See this Apple article: If you forgot your Apple ID password

https://support.apple.com/en-us/HT201487

Then see this Apple article: What to do after you change your Apple ID or password

https://support.apple.com/en-us/HT204071

See also this Apple article: If your Apple ID is locked or disabled

https://support.apple.com/en-ca/HT204106