Amending my 2019 returns already Efiled and accepted by IRS Forgot to apply the overpaid tax amount of 2018 towards 2019 return How to apply for refund of underpayment penalty

[Critter]

Wait until the IRS fully processes your return as this is an error they usually find and correct for you automatically.  They will send you a letter when they have made the correction.  If you have a balance due to pay even after the overpayment has been taken into consideration then make sure you pay it timely.