If you’re new to London, follow “Trains to Gatwick Airport” signs at Victoria, London Bridge, or St Pancras

https://www.scribd.com/document/1077066259/Heathrow-to-Gatwick-Airport-Transfers-Coach-Taxi-or-Train-174457

If you’re new to London, follow “Trains to Gatwick Airport” signs at Victoria, London Bridge, or St Pancras. Ticket machines and staff can assist with route and fares.