When you enter the Form1099-K, you will indicate that it is for self-employment income. Then you will see a screen that says Your self-employment 1099-K income on which you can use the Enter new line of work box to name the business you are in:
Then you can got to the self-employment section and find the business you named and add expenses to reduce the gross income reported on the Form 1099-K down to the net income you received.