I got my 1099-NEC, but they included an accidental payment that I reversed back to them as part of my income. Is there a way to enter that there was a payment reversal?

Report the Form 1099-NEC as you received it and enter the payment reversal amount as a business expense.  

The payment reversal could be entered in the category Other Miscellaneous Expense so that you can enter your own description for the expense and the amount.