Magic won't change your voice, at least not without serious effort on your part. Try singing lessons, voice lessons, and public speaking. You'll learn skills with singing lessons which are absolutely applicable in rap music.
Involve yourself with creative projects, especially writing. Make poetry. Write puns. Re-write things that come to mind with synonyms found in a thesaurus. Add these words to your personal diction, at least at a songwriting level. No matter how nostalgic a piece you've written is, don't include it in your portfolio unless it's an actually good song.
Magic side: Success, determination, and luck are tops. Talent goes a long way, but there are loads more talented and hard-working people than you'll ever hear about. Most people who make it "big" just happened to somehow be at the right place at the right time for just the right person to witness a display of their talent.
But if you don't develop that talent, regardless of whoever you meet, it won't matter.
Even though I find your request somewhat immature, I shall give you a link to a potion that is quite easy to make in order to improve your voice. https://www.spellsofmagic.com/coven_ritual.html?ritual=4227&coven=498
However, this potion shall help you just with voice improvement, but do not imagine that just by doing this alone, you will achieve success. In order to have a very good singing voice, one needs to practice for years and years, study vocal techniques, develop musicality, etc. It is not that easy at all. And then once you reach a real potential, one needs to put itself out there to be discovered, liked, listened... You will try to be successful in a highly competitive field where out of 100 extremely talented and hard-working people, only 1 might make it.
Good luck, though! I'll buy your record if I ever come across it :D
