Hi,
Is it connected via a USB, Jack or Bluetooth?
If connected via a jack or USB, make sure it is plugged in properly. Also, try connecting it to another port to see if it works there. It is also advisable to test the external speaker with another device to make sure the speaker itself is not the problem.
Press Windows key + R, type mmsys.cpl, and click OK.
Go to the Playback tab.
Can you see your external speaker there?
If yes, right-click on it, then enable it and set it as the default device.
If you cannot find it there, then it could be a detection issue.