Did you receive a letter or notice from the IRS stating that you have additional taxes owed? What is the letter or notice number? The number is located in the upper right corner of the first page usually preceded by either a CP or LTR.
See this TurboTax support FAQ for an IRS letter - https://ttlc.intuit.com/questions/3605673-i-got-a-letter-or-notice-from-the-irs
