Clearly the condensate drain is plugged. Unfortunately, I've only needed to run my AC once (when I bought the trailer to make sure it worked), so I can't tell you anything about where it is or how it works. Hopefully someone else will chime in.
I'd start by pulling off the inside cover and seeing what I could see.
1988 Coleman Sequoia - popup (1987-2007)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10