If it looks like the one in the pix below, they are a friction fit, no screws hold them in.
To remove, you take a flat blade screw driver, insert the blade between the light and gasket. Then pry the light out of the gasket.
This type of light is typically sealed and the lamps inside are not replaceable. In this case, you replace with a new oval module.
You might also be presented with a plug in on your existing light, that plug may be loose or corroded which can cause intermittent light operation. Push plug back on and or check and clean and corrosion you might find and retry the light.
If no plug in, then issue most likely is inside the module and replacing the module is the fix.
To reinstall, make sure gasket is installed and seated, then install one end into gasket opening then push and wiggle the remaining portion of module until it is firmly seated in the gasket.
