I received a letter from the Missouri department of revenue tax division stayed they underpaid me for 2022 credits of $1400. How do I add this to my taxes?

You would have to read the notice carefully, because normally they would send you a check if you overpaid on your tax return. Otherwise, they should inform you as to what credit was underpaid and how to rectify the situation. If you could clarify what credit they are referring to that may help us. 

did you already file the state and get the refund indicated on the return?  if yes, you should be getting another check in 2023 from the state for that $1400. there's nothing to report for 2022 since the money is coming in 2023