[Wingerdinger]

First, it would be very helpful to know what year your unit is. You can add your year/make/model as well as your Tow vehicle to your signature to make it easy for each of your posts.
I don't know of any modern RV, say, after 2012 that doesn't already have a winterizing method built-in. I would get on the Keystone web site and find the owners manual.
The winterizing valves are usually in the vicinity of the water pump, and I don't see it in your picture. Find that, and you will probably find your winterizing valve(s).
Mine is in the water heater compartment, accessed by removing four screws from a panel in the bedroom.