Certainly, it isn't easy getting to these valves/connections on any RV--
Sounds like you have a handle on how to fix it, sorry I didn't understand the question.
Most RVs have a valve on the cold water line that does not shut off flow, but is there to direct full flow to the water heater in one position and by turning the handle part way in the other direction, part of the cold water flow is diverted into the hot water line coming out of the WH in order to lower the temp of the water if too hot--a 'mixing valve' may be more descriptive, but it should actually be a '3-way' in that flow comes in and can be sent out in one of 2 directions--direct into the WH or part of the cold flow across to the WH OUT side to mix with the hot water and reduce the temp.
Hope I am not over-working this, but hard to make a picture with words....
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired