How do I setup reminders/to do's in QBs Online?

Hi, @PH99. It's great having you here in the QuickBooks Community. 

Although Quarterly isn't an option from the drop-down menu when creating a recurring template for the rent payment reminders, I can suggest some specifications for making the reminder in QuickBooks Online (QBO). 

You can consider manually determining the monthly interval for the quarterly rent payment. For this, create a recurring check or expense reminder following these specifications. Here's how: 

1. In your QBO account, go to the Gear icon.
2. Select Recurring transactions.
3. Select New.
4. From the Transaction Type, choose Check or Expense.
5. Set recurring template Type to Reminder from the drop-down menu.
6. In the Remind __ days before the transaction date box, choose the most appropriate number of days.
7. In the Interval section:
   a. Select Monthly. 
   b. Select day from the on drop-down menu, and choose the approximate date you'll be paying the rent. 
   c. In the of every __ months, enter 3.
8. Enter other necessary details.
9. Hit Save template.

For future reference, let me add this article about managing your expenses and payments in QBO: Enter and manage expenses in QuickBooks Online.

You're always welcome in the Community should you need further assistance creating reminders in QBO. We're committed to offering ongoing support. Take care.