I made an estimated tax payment on April 18 and it was posted in the Q2 period. Can I change the payment for Q1 or is that up to the IRS?

Good day, @jeffk05.

Thanks for reaching out in the QuickBooks Community page. 

If you made the payments through the EFTPS website, you can contact them and check if they can update the period it was posted. 

You can reach out to them using the phone number posted in this link:https://www.eftps.gov/eftps/direct/ContactUs.page.

If you manually paid the payments through email, reach out to IRS Customer Representative so they can update it for you. 

Let me also share about schedule C categories and how to categorize transactions in QuickBooks Self-Employed. This will provide you with guidelines on how to report your self-employed income and expenses.

Should you have any follow-up questions or concerns, don't hesitate to post again here in the Community or leave a comment on this thread. Take care and have a good one.