TurboTax covers city tax returns during the state tax interview. When you're in the Michigan interview, TurboTax prompts Which cities did you live or work in? To prepare the city return, you'll need to check "I need a Detroit City return" (if it isn't pre-selected) and indicate if you were a resident, a part-year resident, or a nonresident of Detroit. Note that some cities may be pre-selected based on your W-2.
TurboTax will electronically file your Detroit tax return with your Michigan tax return if your Michigan return is electronically filed.