How to get to blown light bulb
I can't be certain from the image provided but it looks like an LED fixture. A lot of times those LED fixtures are made to not have a replaceable bulb (IE the bulb is built into the fixture itself). If that is the case, then the whole fixture would need to be replaced. If you don't have open access to the ceiling (in the case of an open attic above or the like) it appears you need to pry the metal plate off to access the rest of it. Before doing that maybe try turning the plate to see if it unscrews or detaches from a locking mechanism.