Customer failed to properly report 401K rollover on timely filed 1040 for 2019. IRS adjusted to include in income plus 10% early withdrawal penalty over $5K. (im still waiting to see actual irs adjustment). Customer now has proof 401K was rolled over in 2019. What is best option to correct missing rollover by preparing 1040X amended return OR preparing Form 843 Claim for refund??  *note, Subsequent year refund paid off entire 2019 tax plus accruals. I know some detail is missing but any help is much appreciated.     Stevo