I can't open my rear hatch. It appears locked and I don't know how to

Have you tried using the key fob, interior latch, and exterior handle?

Try to take a piece of a soda can and wiggle it around where the trunk attaches to the car, see if you can kinda jiggle it free. This worked for me on my friends car, so it’s worth a try.

Try to forcefully open the trunk. Not the prettiest method but sometimes it works.

Have you been keeping the car clean? If not there could be some weird gunk in the latching mechanism that’s gotten it all stuck.

If none of those work there must be a problem with the physical mechanism of the car. Classic 2000s GM. If that’s the case you will need to take it to your local Chevy or Buick dealer for them to check it out. The Relay was also rebadged into the Chevy Uplander and Buick Terraza so they will be able to take a look at it.