A picture would help. Most likely it is a sealed unit. Although it has a bulb in it you can not replace just the bulb. You need to replace the entire unit. It is possible it has been changed to LED by former owner and they have no bulbs to replace either.
2000 Winnebago Adventurer 32v, P32 Workhorse Chassis 7.4l Vortech, J71 Ultra RV upgraded 67,000 miles