How do I contact a previous owner to remove activation lock from a device

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

https://support.apple.com/en-us/HT201365

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

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 - but you’re short of options.

Sorry, but Apple will not help you with this, nor can anyone here either. At this point, I would strongly suggest that you return it to whom you bought it from to get a full refund.

Then you should ask that someone or return for a refund.

Apple do not give out personal info to anyone.

Sorry Apple do not take part in 3rd party sales.

If you bought a device that is Activation Lock, and you can't get your money back, you got scammed.

Always buy from a reputable shop or new/refurbished directly from Apple.

I certainly understand your wanting to find the owner to return it, and can truly appreciate your effort. At this point, you can either return it to the seller (in case they may know, probably not likely), or bring it to your local law enforcement agency to turn it in (if you feel it might have been lost or stolen.)