This is a common question when using the IOIO, and the answer is easily Googleable. Also, please adhere to the SO guidelines when posting, showing what you have tried, and what you are having problems with.
Servo control is PWM, which is a function built into the IOIO library:
PwmOutput pwm = ioio.openPwmOutput(pinNum, freq);
pwm.setDutyCycle(dc);
pwm.setPulseWidth(pw);