I probably makes sense to amend your 2017 tax return first. If there is no tax withholding shown in box 4 of the code PJ 2018 Form 1099-R, 2018 TurboTax will ignore this Form 1099-R other than to remind you that any earnings shown in box 2a of this Form 1099-R were includible in income on your 2017 tax return. If there are no earnings shown in box 2a, you don't need to amend your 2017 tax return.
