IF you can see the back of water heater and all the lines then look for the line that goes from cold inlet to water heater (bottom) and hot outlet from water heater (top)....that line is the bypass.
Need to close the cold inlet to water heater and open bypass
This can be done several ways...depends on valving used
Cold inlet can be a 3-way valve (cold inlet one way---1/4 turn bypass) and hot have just a check valve
Cold & hot could have 3-way valves (both have to be turned 1/4 to bypass)
If you run RV antifreeze into water heater it will take 6-10 gallons (depending on WH size) just to fill WH tank.
Then come spring you have to flush flush rinse rinse and still have foamy hot water.