I've filed my taxes already, I now need to file RITA. Where to I find that form in my TurboTax online?

The RITA forms could have been prepared as a last step when you prepared your Ohio return.   If you did not take care of RITA, you may find that it would be easier to just use the RITA site.  You need some information from your W-2, and you can file a RITA return on their site.

RITA Web site:  http://www.ritaohio.com/

You can find RITA in the Ohio Cities section.

1. In the Ohio section go to the screen "A few things before we wrap up your state taxes"
2. Select Ohio city taxes
3. On "Do you want to file your city income taxes?" select RITA then Continue
4. On "RITA Municipal Income Tax," tap File Form 37

As Tax Champ xmasbaby0 says, it may be easier to file directly with RITA.