Question about activation lock

If you cannot reset the password of the Apple ID account used, you will need to enroll in account recovery in order to gain access to the account again, see this link and follow the instructions provided

How to use account recovery when you can’t reset your Apple ID password - Apple Support

See if you can recover the ID/password. An iCloud e-mail address is an Apple ID. Use every email address you can think of.

Apple ID - How to find your Apple  -  

Apple ID - Find  -     

Other ways to find your Apple ID

You can check to see if you're signed in to the App Store, FaceTime, or Messages on your iPhone, iPad, iPod touch, or Mac, or check to see if you're signed in to iTunes for Windows on a PC. You can also go to iCloud.com or appleid.apple.com and see if your Apple ID prefills on the sign-in screen.   

If you forgot the Apple ID (iCloud) password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get a Rescue or Notification email option if necessary. Link to contact Apple Support at the end of the 2nd article.

Apple ID - Manage

Apple ID – Forgot Password  *      

If necessary, if you are the original owner, contact Apple. Apple can remove the ID  if provided the required paperwork to include the original purchase receipt with the serial number on it. 

Request additional support for unlocking your device.    -

You used to be able to take the device, the original purchase receipt with the serial number, and a photo ID to the nearest Apple Store (if it has reopened) and have them remove the ID. This may have changed, so call the store before going to make sure they can help.

Genius Bar Reservation and Apple Support Options - Apple.   -