Presumably the iPad is currently locked with an unknown Passcode, or has been reset and is now prompting for the last used AppleID credentials to satisfy the Activation Lock.
Unless you can independently obtain assistance from the previous owner, the iPad will remain inaccessible to you. If you are able to contact the former owner, they will require this information:
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be satisfied:
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, you’ll not be able to defeat or bypass the Activation Lock. With documentary evidence that you are the original owner (such as the original sales receipt showing the serial number), Apple may be prepared to assist - otherwise they and nobody here will be able to help you.