Watford Junction is the closest station to the Studio Tour. From there you can get on a shuttle bus to the Studio Tour, which costs £3 per person for a return journey. The journey takes around 15 minutes.
At the moment all visitors over 11 need to wear a face covering on the shuttle bus unless you’re exempt from wearing one. All visitors are asked to use cashless payment methods.
For more details and bus times check the Studio Tour’s travel page.