Removal of cover of round ceiling light in bathroom

[table]

I would like to change the light bulb of a round ceiling light in my bathroom but I do not know how to remove the cover because there is not screw or button. There is only a small notch but it is difficult to push. Hence, I would like to know if I have to turn the cover or to pull down but I do not want to damage the round celing light

I attach a screenshot of a round ceiling light which looks like this which is in my bathroom