I can't find anything specific about opening case, its possible the side panel is screwed on from the rear and will slide off when unscrewed.
its probable the GPU connection is standard.
if the GPU was installed correctly the TAB should be in the UP position AWAY from the MB. PUSH the tab down until it stops about a 45 degree angle it will sort of push on the GPU forcing it out. dont be afraid just slowly wiggle the GPU out of the PCIE slot and it will come out
I do see some have brackets to hold GPU up but I am not sure about your model as none of the videos show it with side off