To add a recurring payment on EXISTING Payment Forms, the first thing you have to do is add a recurring payment frequency component on your form.
Then select the Payment Form where you added your preferred payment frequencies.
Select Edit Form.
You will now be redirected to your selected form's builder page.
Now, to add a Recurring Payment on your payment form, select Ecommerce.
Look for Recurring Payment Frequencies component, drag and place it into your form.
Select Save Form.
A success message will appear when changes on your form has been saved.
Go back to the list of forms, and select the form where a Recurring Payment Frequency component was added.