Just keep going through the screens until you reach the screen, Here's the income that Maryland handles differently. Then click on the Start box next to Maryland College Savings Plan Contributions (as posted in JeffreyR77's answer above).
If you have already gone through the MD interview, when you go back in to your return you will see the screen, Your 2020 Maryland taxes are ready for us to check. Click the Edit box next to Income. You will be taken right to the screen, Your 2020 Maryland taxes are ready for us to check.
