I had a problem with the light below the waterfall in my original Epic. The dealer had to come dig foam out from the back of the tub to get to that light and replace the led. I guess the same thing would have to happen for your tub. I believe Marquis had a lot of problems with that waterfall light, perhaps because it got very hot from the foam and tub temperatures. My replacement Epic ('08) did not have that light under the waterfall, so I guess they decided to eliminate it.
Probably your best bet would be to call your dealer.