To label your rotation days use the first period in your planbook.  Edit it and type in the day label in the planning area.  This could be "Day A", "Day 1" or however your school labels the days in your rotation.  Set it to repeat based on your rotation and Save. You'll need to do the same for each day in your rotation.

If you have off days or need to bump a day the labels will adjust to continue the rotation.