You can't.
There is no where on the IRS forms to "adjust" a 1098-T. If the 1098-T, you received, is not accurate, just don't enter it in Turbotax or change the box 5 amount at the 1098-T screen to what you think it really is. The IRS does not match your box 5 entry to the copy of the 1098-T that they get.
