Where do i enter business mileage in turbo tax self employed edition?

you need to add the vehicle under 

in part II there is a specific line to added auto info  (actually any vehicle)

click on quickzoom to add the vehicle

it's under the sub-worksheet that you'll enter mileage

You can claim your business mileage expenses by following these steps:

1. Using the magnifying glass at the top of the page search for Schedule C
2. Click Edit or Add if you haven't entered your self-employed income yet
   •  be sure to include Vehicle as an expense type when you are adding expenses
3. If Vehicle is not an expense category listed scroll to the bottom of the page and click Add expenses for this work and choose Vehicle
4. Click Start next to Vehicle on the list of expenses and answer the questions with your information