If you’re transferring from Heathrow, use the RailAir coach or Tube to Victoria, then train to Gatwick

https://jeffreyizjt394.raidersfanteamshop.com/national-express-to-gatwick-airport-routes-prices-and-discounts-2

If you’re transferring from Heathrow, use the RailAir coach or Tube to Victoria, then train to Gatwick. Direct coaches also run between airports at certain times—book ahead.