Rear hatch latch needs to be replaced, how difficult is it? on 2004 Buick Rendezvous

The latch on the bottom of the rear door (trunk) is missing on the vehicle I just was given and I need to replace it so the door will stay closed. How difficult is it and how do I go about doing that? What is the part called?

Asked by for the 2004 Buick Rendezvous