If you have a 1099-K, then you must have some self-employment/business income.
Credit Card Rewards are not taxable, so you do not need to input them in TurboTax. Since they are included in your 1099-K as income then you need to subtract them out of the net profits as an expense.
If you are reporting your 1099-K on Schedule C, then you can enter an expense on the Schedule C as a reduction of costs.
For additional information refer to the following link:
Credit card rewards treatment
