OK, you need to find a song with 'curse breaking' meaningfulness to you. Learn to play it on this guitar (hopefully something fairly simple).

Once you feel like you can play it through consistently enough, that's when you perform the ritual of curse breaking with candles and incense or whatever makes sense to you. You play the song in the magic circle of the ritual, then pour salt over the guitar and in the sound hole. DO NOT TOUCH it again. Use gloves or something to keep from making contact with it from this point forward. Then get rid of it or destroy it (preferably with a fire that reduces it to ashes). That should do the trick and save this cursed world.