Do you agree with what the IRS is claiming, disagree, or don't know?
If you purchased Audit Defense, we can tell you how to contact the company that handles that (intuit.taxaudit.com).
If you did not purchase Audit Defense, you can still get help with your IRS letter from TurboTax free Audit Support Center. To get the phone number, go to the link below, click the blue "Get Help" button, and follow the prompts.
https://support.turbotax.intuit.com/irs-notice/audit-support/
If you explain more about what the IRS is alleging, you may also get some suggestions in this user community forum. But this is a public Internet forum, so don't post any personal info.