Bought a device with activation lock

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Turn off Activation Lock – Apple Support

As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.

Sorry, you’re short of options.

The All Too Common SAD Reality of Buying … - Apple Community

The person who locked it has to remove the lock.

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

There is no way for you to unlock it. And Apple won’t get involved with a private party sale or exchange of personal property. You need to be able to contact the holder of the activation lock in order to get it released.