In addition to the three-flour sourdough I always keep a standard Rye sourdough for all kind of wheat/rye based breads. The instructions to prepare and feed it are pretty much identical.
Stir and put the lid on top leaving a small gap for air.
To feed it add 30g of rye flour 30g of water every 24 hours.
After day one you should observe small bubbles on top of the dough and a light sour smell.
Starting from day four you are ready to use the dough. It should have a nice sour smell and a creamy consistency.
Over time you’ll also develop a good feeling for the water-flour proportion. So add more water in case you think the dough is too dry.