I received a notice from the IRS regarding my 2018 tax return. I purchased Audit defense when completing my return and am unable to download it - who can help me?

I'm unable to download my 2018 tax return for reference and am unclear how to lean on the purchased Audit Defense to assist with the recent claim from the IRS that I misrepresented my taxable income. Can someone please advise on what my options are? Thank you in advance!