Assuming that you mean Skype for Windows Desktop:
First open Skype
Click Tools/Options
On the left, click Audio settings
Click on the Speakers drop-down and select the correct device. Ensure that the volume slider is turned up.
If you're not sure which device to select, choose the first, then click the blue play button. If that doesn't work, select the second device and click play. Repeat until you get it working.
The best way is to uninstall the Skype and install it again. But don’t forget to download a new version of Skype.
After installing it again go to the Skype client program main window
Then,
Tools -> Options -> Audio Settings
Check your audio settings select the device you want to want to use and if you make any changes click the “Save Button”
Hopefully this will help you.