Are you referring to the sound playing when a hit object gets clicked? If yes these are included in skins, and are not separate from the visual side of the game. (hitcircles, gameplay UI, etc.)
And since you're using lazer you can't easily edit skins to swap the hitsounds around. To do that you would need to get the regular client, and copy the hitsound files over to the skin you're using.
Do note that if you're using any of the default lazer skins there is no possibility to change their hitsounds.