Incorrect basis form 8606 for the year 2007

For tax year 2007, my contribution to non deductible IRA was $3K and it was first year I ever contributed to a IRA. I have never contributed after that until this year 2019 and doing Roth conversion. I checked my 2007 form 8606 and it says $4K for non deductible contributions and $2k as basis. So my prior years total basis is $6000. Which is incorrect. It should be $3K in form 8606 for 2007. 

i never took any distribution. 

how do I correct this? 

thanks, 

powerguru