Well, I hate to brag, but my singing is probably what got my drumming out to the public for the last 40 years. It’s gotten worse over the years with age, but I’ve discovered warming up properly helps (and that’s been more constant over the last 15 years). And knowing when to say “I can’t do that” also helpsRapping is just talking with rhythm. We all do that to an extent anyway. The hardest part is going to be learning how to sing. I'd start there, but just a few days probably isn't enough time.