If you add/change fees to a course that has already been created, navigate to the course detail screen for the course you added the fees to and select 1 Copy Course Fees to Existing Classes.
This will give you a dropdown where you can 2 select the time period containing the existing classes that you want to apply the fees to. If you need to do this for multiple times, repeat steps 1-3 for as many time periods you need to copy the course fees to. When you have selected the appropriate time period, select 3 Copy.