After you file

see this webpage

https://accountinginsights.org/how-to-waive-a-substantial-tax-understatement-penalty/ 

this from the iRS

https://www.irs.gov/payments/accuracy-related-penalty#:~:text=For%20individuals,%20a%20s 

 

 

it the penalty is substantial it may be best to consult with a tax pro and let them handle the protest