To reset the LS15 or LS100 headset, there is a small hole on the right ear beneath the earpad (you have to remove the earpad to see this.) Please note, removing the ear pad will not break the headset. In the picture below, that reset button is just above the “R”. You have to insert a paperclip or toothpick, then gently press the button for 3 seconds.
Once the headset has been reset, the trick is to place the earpad back onto the headset by trying to hook it on one side, then start pulling it into place. The earpads seem delicate, but they actually have a good amount of stretch to them so you can pull them back over the lip of the frame.