How do I amend my 2017 return in TurboTax for a Roth IRA excess contribution? I have already filed my 2017 taxes. I will be getting a refund in 2018 for the excess.

I mistakenly contributed $458 to a Roth IRA that did not qualify in 2017.  I am being refunded in 2018 for that amount plus a small amount of earnings ($18).  Since I have already filed my 2017 taxes, how can I amend my 2017 return in Turbo Tax to reflect that amount?  How will I report the refund on my 2018 return?