How do I unlock an iPad locked to owner?

You only have 2 options:

• Gain access to the account it is locked to. You will need to know the Apple ID and Password and if you forgot the password, you will need to have it reset.
• Submit the original purchase receipt from Apple or Authorized Apple seller to remove the Activation Lock. No other third party receipt will be accepted.

How to remove Activation Lock - Apple Support

If you purchased the device used and the Apple ID showing is from the original owner, then it was not properly reset before it was sold to you. That will forever lock the device to them and you would need some way to get their assistance in removing the device from their account. You will not be able to reset an Apple ID that is not yours.

If you see a "Locked To Owner" message, one referring to iCloud locked, or activation locked:

Take it back to the person from whom you received it. Get them to do the things in this support article or ask for a refund --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support There is no way to discover the owner of a device unless they left a message to display on the device when it is turned on, or the person who gave you the device knows them.

Read this article about removing Activation Lock --> How to remove Activation Lock - Apple Support Unless you have the account information that set the lock, the original receipt from Apple, or can demonstrate legal inheritance from a deceased owner, you cannot remove the lock; recycle the device.

From the very bottom of Apple Trade In - Apple :

"Does Apple offer recycling?

Yes. Apple Trade In lets you recycle any Apple device (including devices from Apple-owned brands) at any Apple Store and on Apple for free. That includes your batteries and old electronic products as well as free, on-demand packaging recycling for our commercial, education, and institutional customers. When we receive your device, it will be thoroughly inspected to determine if components can be recycled or reused. Whether recycled or reused, all activities relating to the processing of your device will be managed in an environmentally responsible way."