Screen 24 Form 8606 (Part I) should already have the IRA basis for 2017 and earlier years. ($8,000)

Screen 13 Form 8606 in the lower left Section - be sure to enter the Value of alll.... as on 12/31/18. (Use -1 for Zero, if appropriate)

Assume they ONLY had that one non deductible IRA, the $8,644 should show up as the taxable portion.