Go into Windows Sound Control Panel and unhide and enable Stereo Mix on the Recording tab (right click show all devices). Then select Stereo Mix as the record input in Wavelab audio devices.
Or run a cable set from your computer audio line out to your Focusrite line ins.
Other Focusrite interfaces have a loopback function in software where the computer audio could be routed, but I don’t believe the 2i2 does.