I want to appy some of refund to next year for 2018 where do I show this on 1040 form

To add, change or delete a current year federal tax refund to next year's taxes before you file your tax return -

• Click on Federal Taxes (Personal using Home and Business)
• Click on Other Tax Situations
• Under Additional Tax Payments
• On Apply Refund to Next Year, click on the start or update button

Or enter apply federal refund to next year in the Search box located in the upper right of the program screen.  Click on Jump to apply federal refund to next year

To apply your federal refund to next year, enter it under
Federal Taxes Tab or Personal (Self Employed/H&B/Self Employed version)
Other Tax Situations
Additional Tax Payments
Apply Refund to Next Year - Click the Start or Update button