How do I get a refund of underpayment penalty?

[Mike9241]

see this link. 

https://www.irs.gov/payments/penalty-relief#:~:text=During%20the%20call%2C%20we%E2%80%99ll%20tell%20... 

if it has been paid filing form 843 is required along with providing reasonable cause.

if it's just a bill you received that has not been paid call the number after reading what's provided in this link

https://www.irs.gov/forms-pubs/about-form-843