What does you state withholding have to do with the IRS? The IRS only handles federal tax returns, not states.
Are you referring to state income taxes withheld from your wages and reported on a W-2? If so, the state taxes withheld are entered on a federal tax return as an itemized deduction on Schedule A. And entered on a state income tax return as a tax payment.
Please verify who you are communicating with, the IRS or your State? How were you informed you needed to fax something to them? By a phone call, email or did you receive something in the mail?
What exactly are you trying to send?