You don't need to do anything if you answered the questions correctly in the Federal return. After you enter the 1099-R in the Federal return, you continue on and you are asked the source of the income. You check that it's retirement from active duty military service, enter the MD amount below if it's not already there. On the next screen you choose that it's a nonqualified pension. The correct amount transfers to the 502SU in the state.
If you need to go back to the federal return to make changes,
click on the Federal Taxes tab, then Wages and Income just below.
Scroll down to retirement income and update the 1099-R section.
Edit the 1099-R in question and go back through the interview to answer the questions.