In the default configuration, C1 + the left dial should zoom. Of course you should be in one of the modes that support zooming. You can configure the combination of the keys in a dedicated section.
H, Danyrr. Thank you for reaching out. The right Camera Control Dial on the DJI RC is the button used for zoom control while the left Gimbal Dial is used to control the tilt of the camera. You may see the functions of other buttons on this link: https://dl.djicdn.com/downloads/ ... Manual_v1.0_en.pdf. Please don't hesitate to reach us if you have any inquiries or concerns. Thank you for your valued support.