how to correct I-485 wrong birthday

During my finger print, I was asked to confirm my personal information. I found that my birthday in the system is not right. Because they could not correct the wrong birthday at finger print collection site, I was told to call USCIS's 1-800 number to straight thing up. The lady took my call told me that she couldn't correct the data and she asked me to write a letter to Vermont Service Center where I filed my I-485. I was wondering if someone has the same experience or knows how to correct wrong personal information related to I-485. Thanks.