Was there a penalty on your tax return line 38? You needed to fill out form 2210 to eliminate or reduce it. To show when you made the conversion and when you paid the estimated payment.
Don’t know if you can amend for that.
You can go to Federal Taxes tab or Personal tab, under Other Tax Situations and select Start by the Underpayment Penalties. You will answer a series of questions that may reduce or eliminate the penalty. Or you can elect to have the IRS figure the penalty for you. It's form 2210.
It's under
Federal or Personal (for Home & Business Desktop)
Other Tax Situations
Additional Tax Payments
Underpayment Penalties - Click the Start or update button
Here is a blank 2210 and instructions. Maybe you can figure it out by hand to give the IRS.
IRS form 2210
https://www.irs.gov/pub/irs-pdf/f2210.pdf
2210 Instructions
https://www.irs.gov/pub/irs-pdf/i2210.pdf
