Once in the workout editor (Menu Bar Workouts-List-New), you will see a number of different buttons. One of these buttons is "Duplicate Weeks." Keep in mind when duplicating weeks, it will also copy any exercises you have programmed for that week.
Once you press duplicate weeks a pop-up will appear asking you how many times you would like to duplicate this week. Note: the number that you put in will be in addition to the week(s) that already exist. For example, above there is one week and below we will duplicate it 4 times, for a total of 5 weeks