Running and debugging are controlled from the main toolbar:

Selecting a target

When a Flutter project is open in the IDE, you should see a set of
Flutter-specific buttons on the right-hand side of the toolbar.

Note:
  If the Run and Debug buttons are disabled, and no targets are listed,
  Flutter has not been able to discover any connected iOS or
  Android devices or simulators.
  You need to connect a device, or start a simulator, to proceed.

Locate the Flutter Target Selector drop-down button.
This shows a list of available targets.

Select the target you want your app to be started on.
When you connect devices, or start simulators,
additional entries appear.

Run app without breakpoints

Click the Play icon in the toolbar, or invoke Run > Run.
The bottom Run pane shows logs output.

Run app with breakpoints

If desired, set breakpoints in your source code.