Under User variables check if there is an entry called Path:
    
      If the entry exists, append the full path to flutter\bin using
; as a separator from existing values.
      If the entry doesn’t exist,
create a new user variable named Path with
the full path to flutter\bin as its value.

You have to close and reopen any existing console windows
for these changes to take effect.

C:\>where flutter dart

C:\path-to-flutter-sdk\bin\flutter
  C:\path-to-flutter-sdk\bin\flutter.bat
  C:\path-to-dart-sdk\bin\dart.exe        :: this should go after `C:\path-to-flutter-sdk\bin\` commands
  C:\path-to-flutter-sdk\bin\dart
  C:\path-to-flutter-sdk\bin\dart.bat

C:\>where flutter dart