How do I edit serving size on incorrect food items?

Loonyb1n

Hi there, when I use my bar code scanner, I sometimes find that the information is outdated on the nutrition breakdown. For example, I just scanned a soup and the serving size as well as carbohydrate amount is different from the label to the app. I click the "missing/wrong nutrition" button, click the check box about serving seizes but then I can't actually add a new serving size. It's locked to whatever is already there. How do I get around this so I can contribute accurate information to the community?