By responding to TurboTax as TurboTaxListBr described and indicating that $100 of the contribution will be returned, TurboTax will automatically report the $100 on Form 1040 line 21 as Other income. This is necessary because the $100 had been excluded from the amount in box 1 of your W-2.
And when you get the code 2 2018 Form 1099-SA reporting the return of the excess contribution, you'll enter that into 2018 TurboTax. Any earnings that accompanied the return of the $100 excess contribution will appear in box 2 of this Form 1099-R and will be taxable as Other income on your 2018 tax return.
