go to Forms mode Open Form and put 2210 in the search bar to bring up the Form 2210 calculation which is generating the penalty
even if you meet the safe harbor in total for the year if it wasn't even over the year you could have an underpayment for one of the quarters
if your income was uneven and in particular later in the year you can adopt the Annualized Income method to line up uneven ES payments with uneven income. Go to Other Tax Situations / Underpayment Penalties to work through that or other options on Form 2210.,
