Open the Task Properties by clicking on the task.
Click on the "+" icon on the Set Date row
By default, every task is set to Don’t repeat. Here you can select the option to repeat tasks every day/workday/week/2 weeks/month/3 months/6 months/year.
Click on Add.
Note that the start and due date must be set on the same date, if not, the repeat function will start after the due date.