I have already completed my federal and state income tax return, how do I do just my local tax return online?

See this TurboTax support FAQ for supported city/local tax returns - https://ttlc.intuit.com/community/returns-and-forms/help/which-city-tax-returns-can-i-do-in-the-turbotax-state-program/01/25578

What state, what locality?

 

Most Ohio and Mich cities have a web site where you can file your city return.

 

Just google (your city name) income tax.

 

You can't do a city return in TurboTax (TT) without first preparing a TT federal and states return (you don't have to file state & federal thru TT, but you do have to prepare (and pay for) them.