Illuminated switch has loosened
I'm not familiar with this scope, but most switches have round, tightening fasteners that can be retightened, if you can get to them, which requires disassembly. Scopes aren't usually made to be serviced, so that can be trickier than it seems, but with a good set of screwdrivers, you may be able to do this. Certain parts of the scope, however, may be machine pressed, and not allowing easy disassembly. If you can get to the switch fastener, you can probably tighten it, unless it was rivited, which I haven't seen.
If you have a gun club in you area, one of the fellows there might know how to fix it, so you might check out that avenue.
Good luck, and hope this helps.