There are no Siam Park buses from this area. You need to get on a TITSA Bus for Los Cristianos, the 473 or the Express 477 (quicker, less stops).
When you arrive at Los Cristianos Bus station, you can pick up the free Siam Park Buses that regularly go by. They are open Top London Buses, painted Blue in Siam Park colours. They will take you to the main gate and return you to the bus station afterwards, where you catch the same bus back to Los Gigantes.
The park opens at 10am and the buses from Los Gigantes are every half hour from 8am (473) and every hour from 9.15 (477)