If you have made the switch to charge upfront, you will no longer be able to switch to per creation.
Before switching the payment type on your account, make sure to communicate the change to your patrons! Once you've shared the news of the switch with them, here is how to change your payment type for your account:
Step 1: From your creator page, navigate to the top of your creator page and click "edit your page."
Step 2: You might also see this view instead. To edit your monthly or per creation status, click the "payments" tab.
If you're switching to "per creation," enter what it is that potential patrons will be paying for when they become your patron. If you're switching to "monthly," you will not need to enter what it is you create.