I'm trying to deploy the flutter app, and now I'm trying to update the app's version number. Currently, it is "version: 1.0.0+2" but I just go with 1.0.0+3 for this time?
You need to increment both values. So after version: 1.0.0+2
it may be version: 1.0.1+3
or anything else. Information about updating the version number in Flutter can you find on flutter.dev.