There are some counterintuitive rules regarding retirement distributions depending on their tax preferred treatments.
See 2020 Publication 525: Taxable and Nontaxable Income, page 11, first column: Excess distributed to you.
If the distribution was for a 2019 excess deferral, your Form 1099-R should have code P in box 7. If you didn't add the excess deferral amount to your wages on your 2019 tax return, you must file an amended return on Form 1040-X. If you didn't receive the distribution by April 15, 2020, you must also add it to your wages on your 2020 tax return.
In the 2020 Instructions for Forms 1099-R and 5498, page 18:
P—Excess contributions plus earnings/excess deferrals taxable in 2019.
See the explanation for Code 8. The IRS suggests that anyone using Code P for the refund of an IRA contribution under section 408(d)(4), including excess Roth IRA contributions, advise payees, at the time the distribution is made, that the earnings are taxable in the year in which the contributions were made.
You will need to get a copy of the 2019 tax rules if you do not already have the CD/Download in order to file the amended return.
For more information, see: How do I amend a 2019 return in TurboTax?
