Note that there are two ribbons that need to be disconnected here, not quite sure why these are not mentioned here as they need to be disconnected by lifting the white flaps to release the ribbons or it will likely cause damage. Once these are released then the two parts can hinge open and then you can access the battery to remove it.

The two ribbons are a little tricky to reconnect, you may need tweezers to put them in place. I suggest propping the two parts of the case open leaving both hands free to re-attach them, you will need to use a spudger to push the flaps down on the ribbons. Be careful to push the ribbons straight into their connectors before folding down the connector flaps.

I would strongly recommend updating the instructions with this additional information.

Interestingly on my Mac mini there was no torx screw holding this on at all, it was just attached to the logic board. There isn’t actually a screw hole to screw it into on the logic board as it appears to be a river of some kind instead.

A few people have commented here about having to use a lot of force to get this out, but make sure that all of the black area at the back of the case are not being covered by your fingers as you try to push it out, it came out quite easily for me once I realised I had my fingers on it!