1. Rest.
2. Quack (doctor)
3. Sing lower or higher as the case may be.
4. Sing quieter if necessary
5. Voice coaches MAY assist you not to wreck your voice, but beware beware beware they may want to turn you into a plastic opera singer and wreck whatever it is about your singing that is attractive (if it is).
6. If you HAVE to sing this week, Strepsils, or Meggezones, or Vocalzones - but you WILL pay the price.