How to remove activation lock

If you can't reach the previous owner whose ID is on the device and have them go to https://www.icloud.com/find/, erase the device, then remove it from their account, then the device is useless. Apple won't unlock it.

Turn off Activation Lock - Apple Support.  *

Is the iPhone locked to an old apple id of yours which you cannot access? First, try and recover that Apple ID via iforgot.apple.com

If you cannot recover the account and you have valid proof of purchase information you can  start an Activation Lock support request.

If the iPhone is locked to someone else's Apple ID you should ask them to remove the lock, no one else is going to do it for you. Activation lock is one of the best theft deterrent systems out there, only the original owner can remove it, Apple will not do it for you without proof that you're the original owner.

Hope this helps!