how do i convert stereo into mono again?

......

Use any sound editing program, like fucking SOUND RECORDER THAT CAME WITH WINDOWS FOR GAWD'S SAKE, choose Save-As, and pick mono instead of stereo.

Rip out one of your speakers...

Remove one channel.

Congratulation! Now go next stage!
STAGE FIFTH OBJECTIVE: To be destroyed Massive Armament Complex. Also to 300,0000 points acheive!