You can make the change to apply your refund to next year estimated taxes by following these steps (if you are already in the File stage, you will have to go back a bit by clicking these tabs) - see attached screenshot
- Log into your account and click Take Me to My Return
- Choose Federal Taxes (or Personal if using Self Employed full version)
- Select Other Tax Situations
- Scroll down to Additional Tax Payments
- Select Apply Refund to Next Year
- Proceed through the prompts
