STP please help on tax question!Thank you

I got a letter from IRS saying one of my dependents Tax Id didn't match and they reduced my refund amount. I found out I typed a wrong number. They asked me to contact them if I think they were wrong. So what do I do now? Do I have to fill out another form to change to the correct number? do I have to go through the whole form again? I use Turbo Tax but don't know how to correct a wrong number. Or should I call INS to tell them the correct number? Thanks