The letter from the iRS you received explains in detail why the IRS believes you owe the taxes for 2018. Is the IRS correct?
Did you purchase Audit Defense for 2018? If so, contact TaxAudit.com at intuit.taxaudit.com or by calling toll-free (877) 829-9695.
If you did not purchase Audit Defense then you can use the TurboTax Audit Support Center to assist you with understanding the IRS letter you received and recommend what your next steps should be - https://support.turbotax.intuit.com/irs-notice/audit-support/