You are going to need to request a copy of the original return from the IRS. The only way to amend an original return is to have an exact duplicate in the system.
You would need to request a copy using Form 4506. Then, once you receive the copy, you enter the return in 2017 TurboTax Business exactly as it was. Once that is complete, you would go through the amend process in the program.
I've included the link to Form 4506 below. I know this is a tedious process, but I know of no other way to do it with more efficiency.
https://www.irs.gov/pub/irs-pdf/f4506.pdf