If you have already deleted the device from your AppleID account (i.e., it is no longer visible in your device list), there is no method at all by which you can remotely remove the Activation Lock. In this situation, the iPad must be returned to you.
With the iPad back in your possession, you can sign-in to the iPad using your AppleID - which will re-associate the iPad with your account - after which you can properly erase the iPad and deactivate the Activation Lock. If the iPad cannot be retrieved, either the new owner must accept that the Activation Lock cannot be resolved - or you will need to provide your AppleID credentials (the latter is not recommended).
If instead the device has not already been deleted from your AppleID - and the iPad is still visible within your account, you can remotely remove the Activation Lock.
The available procedures for removing the Activation Lock using the Find My service, along with preparing a device for disposal or reuse, are documented here:
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support