A CP2000 is a notice that the IRS has income recorded for you that you did not report.  Read the letter carefully.  You may have forgotten to report a W-2 or a 1099-MISC, 1099-R, 1099-B, or other income statement.

If you did leave off some income, then you probably owe some tax, but maybe not as much as the IRS thinks.  They know about your income but not about deductions or special circumstances.  Start by preparing an amended return with the extra income added.  If the amount you owe matches what the IRS says, mail them a check, but don't mail them the amended return, they will correct your record for you.  If you find that you owe less, then mail a check for the lower amount AND the amended return to the address in the CP2000 notice (not the regular amending address) along with a letter explaining your mistake and new calculations.

If you disagree that you forgot to report income, you will need to write a letter back ASAP.  Be very aware of any deadlines in the CP2000 (usually 30 days or less).  For example, sometimes a person finds that they are the victim of identity theft and their SSN has been used by someone else to get income.  Whatever has happened, if you think the income was not yours, send a letter explaining the situation before the deadline.  I recommend using a mail service with tracking and delivery confirmation like US mail with delivery confirmation, UPS or FedEx.

Also see this IRS article:
https://www.irs.gov/individuals/understanding-your-cp2000-notice

If you purchased the Audit Defense product, you should contact that company and let them assist you with this.  If you did purchase it, we can tell you how to contact them.

If you did not purchase Audit Defense, you can get help in this user community forum.   You can also phone TurboTax free Audit Support Center, if necessary, on Monday.  Here's where to get the phone number:
https://support.turbotax.intuit.com/irs-notice/audit-support/