Line 2 should have been the carry over basis from line 14 of the last prior 8606. If you did not do that AND you have not taken ANY Traditional IRA distributions, then I would simply file a 2019 8606 with the correct carry forward basis in line 2 and 14 and include an explanation of the change. (You probably should file an amended 8606 for each year, but I doubt that the IRS will care. And there is no penalty for amending an 8606.)
If you HAVE taken a prior IRA distribution then the 8606 filed with that distribution and the resulting taxable amount on your 1040 would be incorrect, requiring an amended 1040X and 8606 for that year and amended 8606 form for each following year.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
