You do that in the FILE section when you are ready to file your tax return. You cannot change how to receive your refund after you filed.
When you file a tax return is when you enter the bank routing and account number for the direct deposit of a tax refund.
If you have filed a 2019 tax return the method of receiving any tax refund cannot be changed. If the bank routing or account number is incorrect for the direct deposit the deposit will be refused by the bank and returned to the IRS. The IRS will then mail a refund check to the address entered on the tax return.
If you already have your own debit card then choose the direct deposit option in the FILE tab and enter the routing and account number for the card just like you would any other bank account.
If you don't have a debit card already then buy a pre paid card for $5 at almost any store to use OR choose to pay the TT fees with the federal refund (when efiling opens in January for the 2020 returns) for an extra $45 fee to get a new Turbo debit card.