Judging by that list of parts I suspect that what you have there actually does the same job as a conventional servo, by comparing two pulsed signals (one from the RC receiver, the other generated from the servo position). In that case, what you want to find is the input that provides its steering control signal, and find what sort of signal it needs. At a guess, the pin named 'input' would be a good place to start. If this is pretending to be an ordinary servo, you might find it's expecting a conventional PWM signal which your Arduino would be able to emulate quite easily.