If you filed an incorrect 2017 tax return because the taxable amount determined on Form 8606 was incorrect, you would amend your 2017 tax return to pay the tax that should have been paid.
Because any balance in basis carries over from one year to the next, it's really impossible to know what should have been reported without knowing all of the transactions that have occurred. As I understand it, the first ever nondeductible traditional IRA contribution you made was for for 2015. If yo provided a listing all of the month, year and amounts of contributions, the year for which those contributions were made, dates and amounts of regular distributions (if any), month, year and amounts of Roth conversions made in 2015 through 2018 and your year-end balances in traditional IRAs for 2015 through 2018, I could recreate all of your Forms 8606 and tell you what should have been present on each. Anything else would be based on incomplete information, so I'm not going to make any guesses.
