"If an affected taxpayer receives a late filing or late payment penalty notice from the IRS that has an original or extended filing, payment or deposit due date that falls within the postponement period, the taxpayer should call the telephone number on the notice to have the IRS abate the penalty."

https://www.irs.gov/newsroom/irs-announces-tax-relief-for-victims-of-severe-winter-storms-flooding-a...

Update:  Congress repealed the funds IRS needs to answer the phones.  Call Kevin McCarthy's office instead.