how can i remove the activation lock on my ipad mini

ONLY w/ the cooperation of the AppleID owner who last set up the device.

Presumably the Ex ???

They will need to perform the following actions:

How to remove Activation Lock - Apple Support

If the iPad was purchased from a third party, then only the original owner will be able to unlock the device. The Activation Lock is due to the device either not being erased correctly before being sold or that it is stolen and the owner has locked the device, but still able to track it.

The link provided to remove the Activation Lock will only be useful if the device was purchased from Apple by you and you also have the documentation showing the original invoice including serial number of the device. Apple does not get involved in third party sales where the device is locked by the original owner.