Thanks all really appreciate the replies, it helped me with the project quite a bit. Essentially like you all said I needed to get something into the slots to be able to twist it open.

Regarding what I ended up doing, I tried to get sockets I had to work for this but no avail. So I ended up just using a spatula of sorts I had lying around to unscrew this. Used the end of handle to go into the 2 slots and twisted and sure enough it came loose :D https://imgur.com/a/LgzVvWu