How do I swap audio output of the left and right speakers?

You could get a cable that splits into two channels and one that merges them again. Then just swap the channels inbetween. For example this kind and this kind, if I read correctly... cables and audio isn't my thing :p Anyways, something along those lines should work maybe work?

I experienced this same problem with a set of Logitech speakers whose cable wasn't long enough to be placed the right way round on my (long) desk - they seem to assume that the PC will always be underneath the monitor, or on the right hand side.

My sound chipset doesn't have any support for swapping channels, so I had to make an adapter plug/socket combo. Find someone who can use a soldering iron, and get a 3.5mm plug and socket, and several inches of stereo audio cable - should be done in less than 5 minutes.

Some soundcard drivers actually have an option to swap the left and right channels in their Control Panel applet (eg. A Realtek adapter I used to have did). I imagine this might have to do with the features of the specific sound chipset. Other drivers/chipsets don't.

Some games/applications have software methods to swap the left and right channels in their settings/configuration window/file (eg. Final Fantasy VII PC, Winamp). Others don't.

The only guaranteed-possible way to swap is to physically swap the wires/speakers in hardware.

Most media player software should be able to do it for you, so at least you can listen to music and watch movies properly — this should solve at least part of your problems.

Here is the solution in VLC player: Audio > Audiochannels > Reverse Stereo.