I would like to declare my income and expenses from my professional income (Part 3B) and not from the business income (Part3A). How do I change it to 3b on turbotax?

If when you started the self-employment part of return, you selected "Other (business)" instead of "Professional", there's no way to change it afterwards. You'll need to delete the business and do it over again, making sure to select "Professional" at the start.

To get back to the self-employment section in TurboTax Self-Employed Online, use the “Find” (magnifying glass) tool and search for “self”. Then select “Self-Employment Summary” from the list and click on the “Go” button to get back to the self-employment section. There you can delete the incorrect business statement, and then start a new one.