I recently retired, and withdrew all of my contributions from a Roth 403b. Surprisingly, 20% was withheld from this distribution. I am 67 this year. How do I declare?

To enter, edit or delete a form 1099-R -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On IRA, 401(k), Pension Plan Withdrawals (1099-R), click the start or update button

Online editions -

On the screen Did you get a 1099-R in 2024? Click on Yes

On the screen Let's import your tax info Click on Change how I enter my form
On the screen How do you want to add your 1099‑R? Click on Type it in myself

On the screen Who gave you a 1099-R? select the type of 1099-R you received and Continue