I sold my iPad and the new owner is saying it has an activation lock

You need to help/contact/re-connect to the person you sold this iPad to and both of you need to follow these instructions.

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

Best of Luck to You!

You don't.

the person who locked it has to remove it.

If they refuse to do so or can't, the iPad is useless to you.

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