Depends how technically inclined you want to get. First things first, if you want to try to preserve your programming, get your SD card or whatever storage medium the HMI uses out of it.
Now, go up to the screen and shine a flashlight right on the screen and try to make anything out. If you can make out screen contents, then you may have gotten lucky with only the backlight showing errors. If not, then the screen may be messed up entirely. You can try ordering just a replacement screen and try installing it yourself if you want to tear it down, otherwise you may be stuck with buying a new one. (REMEMBER TO SAVE THAT SD CARD, DONT THROW IT OUT!)
Before you go inside the HMI, disconnect all power to it. If you can, try turning it back on if it has a switch or button to discharge any capacitors to reduce likelihood of getting shocked. Otherwise, you may want to wait about a week before attempting to service it for it to discharge some. (Unless you like being shocked, I won't judge)
If you can, remove the HMI and unscrew the back cover and check for signs of obvious water damage. You may be able to get it off with isopropyl alcohol.
The
app being unresponsive may clue us into another problem with the HMI.
Forgive me for thinking out loud here. I urge you to also get a second opinion. You may want to contact Red Lion to get their opinion on it as well, though they will likely tell you to replace it.
Also, could you see any water on any components when you opened it?
Also, if possible, you should back up your HMI using Red Lion's Crimson software, just in case things go south or you want a quick backup, unless you're going to Red Lion themselves to replace it. There is likely special firmware for the car wash in the HMI and a standard Red Lion Replacement won't have this programming by default.
