At some point I was asked to enter non-taxable income, such as child support. I can't find it now and need to edit. Anyone know how to get to that screen?

I don't believe that would ever be a question on your federal tax return.  There may be state tax benefits that depend on your household income including non-taxable items.  Since I don't know what state you are filing, I can only suggest starting the state interview and running all the steps in order until it comes up.

There is a question about nontaxable income in the state sales tax deduction, and on certain state returns.

To check the state sales tax deduction:

1. Select Federal from the left side menu.
2. Select Deductions and Credits toward the upper left. 
3. Scroll down to Estimates and Other Taxes Paid
4. Expand the section, click Start/ Revisit to the right of Sales Tax.
5. On the first screen, select Try Sales Tax Deduction anyway.
6. Select Easy Guide on the next screen.
7. Continue until you get to Nontaxable Income.
8. Answer Yes, and review what you entered. 

If this is not where you entered the nontaxable income, it would be in your state interview. If you need more help, respond back with the name of your state.