The following procedure will help you back up/export the configuration of a dvSwitch:

1. Bring up the Networking inventory using the vSphere Web Client by using the key combination Ctrl + Alt + 5.
2. Right-click on the desired dvSwitch, go to Settings, and click on Export Configuration...:

3. In the Export Configuration window, you are allowed to either export dvSwitch along with the port groups or just the dvSwitch. Choose the desired option, supply an optional description, and click OK.:

4. On the Confirm Configuration Export dialog, click Yes to confirm the action:

5. Choose a hard disk location on the client machine to save the backup file and click Save:

6. You should see an Export configuration of the entity task complete successfully in the Recent Tasks pane.