Use two lines at the W-2 screen, for boxes 15-20.

On the first line Put the state info in boxes 15- 17 and Columbus in boxes 18-20.

On the 2nd line, put OH in box 15, leave 16 & 17 blank and put the Delaware info in boxes 18-20.

You normally only have to file a return in the city you live in. It is not necessary to file one in the city you work in, if different. Your employer will remit withholding to the city you work in, but you do not file a return unless you're claiming a refund or your employer didn't withhold enough ( both highly unusual). The city you live in will allow a credit or partial credit for the withheld tax you paid to the work location city. 

TurboTax (TT) does not automatically prepare a city return, you must initiate it. At the screen, in the Ohio program, titled 
 "A few things before we wrap up your state taxes"
      scroll down to Ohio City taxes. 

You  cannot efile a city return.  It must be printed and mailed.

Columbus is not a RITA or CCA city, but Columbus will accept a CCA form.

I actually find it easier to fill out a city return by hand or at the city, CCA or RITA web site, than to use TT. Things don't happen automatically and you need to know what you’re doing. The actual  RITA/city forms are easier to follow than the TT interview.  

https://www.columbus.gov/incometaxdivision/