If using a VEX cortex, a continuous servo is just like a 393/269, but with a built-in controller!
I am sure that the VEX motors use the PWM protocol, so most servos should work.
so if using natural language, try startMotor(motorPort/name, speed);
There's a direct equivalent with vanilla RobotC but you should be able to figure that out with ease.
Just remember, it's just like driving a 393 programmatically