Refer change over, quite possibly a stupid question....

Leave your propane tank/tanks open/on. Set the refer to auto. It will run on propane until you plug in the shore power. The refer will do all the switching.

FYI. If for some reason you've unhooked the propane cylinder, say to fill it. You'll need to light a stove burner to draw the propane up the line. That will be enough to start the fridge on propane.