How do I release the motherboard from some strange metallic thing?

So I decided to open up my acer predator 17 (2016) because it's broken-ish and I'm trying to check the RAM modules, that are for some reason on the other side of the motherboard. Unscrewing this took me two days. Now this metallic piece (see pic) is my last hindrance and I just can't budge it out, it barely moves and disassembly guides don't seem to mention this thing

Pic: https://cdn.discordapp.com/attachments/347779708173156352/497485496931450910/20181004_210806.jpg

Edit: I probably should mention I have near 0 knowledge about computers