To remove the activation lock you can either remove it with the correct Apple id and password
To remove if you have the correct apple ID and password
Remove Activation Lock on the web if a device is offline
- Go to www.iCloud.com/find.
- Sign in with your Apple ID and password.
- At the top, click All Devices.
- Select the device that you want to remove from iCloud.
- Click Remove from Account.
Or if you are unable to do so, and you have proof of purchase, you can apply for Apple to remove the activation lock
See this guide:
How to remove Activation Lock - Apple Support
The step to remove without knowing the Apple ID is under Start a support request
then "Get started" on the next page
Here is the direct link:
https://al-support.apple.com/#/additional-support
Good luck!