The income you gave back to customers or clients for your Schedule C business is entered in the Income section of the business, along with any 1099-MISC or cash income amounts.
Click on the thumbnail picture below for a visual reference if you are using TurboTax Self-Employed online.
To go to that section of your return, use these steps:
This will take you to the Schedule C section where you can either Edit the business that you have already entered. When you edit the business that is already entered, you should find a blue link Add income for this work. Use this link to choose Rebates/refunds paid and enter your information.
Note: It may be necessary to log out of your return and then log back in to see the Rebates/refunds option in the Income section.