When editing a route, you can adjust the days of the week that a route runs.  Click on the REPEAT indicator beneath the route name.

By default, a route will be set for Monday-Friday every week.  To change the days of the week, click to de-select the days that the route should NOT run.

In this example, the route runs on Monday, Wed and Fri.

You can also change the repeat to monthly and adjust when in the month the route runs.

Click on the save icon.