changing toilet seat on wall mounted toilet
Look at this video starting at about 11 min 30 s. Grohe wall mounted toilet

EDIT I see a screw exposed under the swing away cover in the picture posted. I would assume that unscrewing it would release the fitting holding the seat.

It might be wise to consult the landlord even before a seemingly simple change of a toilet seat. Maybe his staff  know how to do this and would do it for you.

EDIT2 Have you looked or felt under the bowl to see if seat bolts are visible? See What kind of tool do I need to access this bolt?