You can add the location where MiniZinc was installed (usually somewhere in the Program Files folder) to the PATH in order to run MiniZinc from the command line.
But you should also be able to set parameters in the IDE. When you run a model that requires input, the IDE should ask you for the missing parameters. If you have loaded the .dzn file into the IDE, the parameter dialog will also include a drop-down menu where you can select the .dzn file.
Cheers,
Guido