How to change target emulator in Android Studio?

Click Edit config beside run app.

Click Run → Edit Configurations...

Then uncheck Use same device for future launches

As mentioned by @B-GangsteR, you can also launch your app on multiple devices at the same time. To do this, select targets using ctrl key.

In Android Studio 3.5 or above, the "Deployment Target" part of the configurations dialog has moved into the main toolbar.

Note that even if "Use same device for future launches" is unchecked, you can't launch app on other device while it is still running on first device. So you've got to

• terminate app on first device before running on another device,
• or kill adb process (it will restart),
• or run your app on multiple devices at the same time from the start (when choosing target, select multiple targets using 'ctrl' button or 'ctrl' + A)