Create Salesforce Tasks That Recurs Quarterly

 In order to adjust the Task frequency, the Task page layout must be updated and the setting selected to Enable Creation of Recurring Tasks before following the steps below.

To set a Task to reoccur quarterly 

1. From the Tasks tab, select the drop-down arrow and click New Task.
2. Enter the Task general information.
3. Below Due Date, check the box Create Recurring Series of Tasks.
4. Choose the frequency Monthly.
5. Choose every 3 months
   • In Lightning Experience, set Repeat to Custom and choose 3 months.
   • In Salesforce Classic, select on # day of every 3 months.
6. Choose the start and end date for the recurrence.
7. Save.
   
    

Using the similar steps, you can set the recurrence task on a semi-annual basis by changing the value to '6' months.