how do I reset an ipad I just bought?

Reset how - and for what purpose?

If new, the iPad should be ready for use. If you need to reset and restart the initial set-up:

Settings > General > Reset > Erase All Content and Settings

If you have acquired a previously owned iPad, that is Activation Locked, you will need the assistance of the previous owner...

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.

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

This should have been done by the seller.

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

“You get what you pay for”.

This iPad may have been previously stolen.