You can report your income from self-employment and from form 1099K in Step 3 - Lets’ talk money. If you do NOT have any other income, you can choose Letter from a Payer. If you DO have other income, just choose the other income document(s) that you have from the drop-down menu without choosing "Letter from a Payer".
Once you fill in the income documents that you have, you will reach the section ‘Other income’ and there you should select the income type as ‘Fees/Commissions’.