Earlier I was asked to enter business mileage for my personal vehicle. I made an error in entry (decimal was ignored), now I can't find where to change it.

You have to edit your business entries, and on the screen that says Your (name of business) Business, choose the Business Vehicle Expense option. Work through that section and you will see where you can edit your business mileage.

go back to schedule c. the worksheet for the vehicle should be there. I don't know if there is a faster way to get to that worksheet rather than going through schedule C from the start. it will be the link on the business expense page "cars........................."