Are they LED lights? If they are, you might have a problem. We asked at the factory how to change the light bulbs in those fixtures should they ever burn out, which they haven't. We were told we could not. They are LED and should last the life of the trailer. If they are not LED, I hope you find your answer.
We have a mixture of LED and regular lights in our trailer. The regular ones have those little slidey covers that come off. The LED do not.
It's possible that the light went out for some reason other than the bulb burned out, especially if it's LED. It could be a wire or something.
2012 Cruiser Sahara 330SS
2015 F250 Super Duty diesel