I put my self employment income on my return. I received cash. At the end before I submit, it's asking me for explain my explanation of inventory change. What is that?

Please go back to the Business tab

Scroll down to "Inventory/Cost of Goods Sold"

If you do not have inventory, the "Do you have inventory to report?" screen should show "NO"

Go through that section to verify that "supplies" were not entered that way. 

Continue to see if there is a beginning and ending inventory value and adjust if necessary. 

Hi there and thanks for your reply. Unfortunately, I didn't get the alert you replied and already submitted my return and it was accepted. On my sch c, although I accidentally said yes to inventory. There are no numbers on any line in section 4 from line 33-42. Do you think I have anything to worry about? On my explanation I just said I was paid in cash by customers for 2024. 

Sorry I meant there are no values in section 4 of my sch c. Starting from line 35-42. On line 33 I accidentally chose b. And 34 I chose cash. Oh I hope I have nothing to worry about.

Since you have already filed your return, you'll need to wait to see if you hear from the IRS. If so, you can explain the error. Otherwise, be sure you fix this next year.