I am dissolving my LLC with this return. How do I notify on 1040 or Schedule C that this is the final return with the business?

Business & farm

To dispose of your single member LLC business in TurboTax:

Type sch c in the search box and click search.
Click on Jump to sch c.
Edit the business you are disposing.
Click on Business Profile.
On the Let's confirm your business info screen, scroll down to Disposed of Business in Current Year.
Continue with the onscreen interview.

See the screenshots below.