How do I put out an Alarm needs service light

I would start with a scan just to see if there is a set fault code that relates to the immobiliser, if there is a fault, the light will not come off until it is rectified.

Have it checked for siren and sunroof communication codes. If there is a fault in the LIN bus communication then the siren is faulty. Usually the sunroof will not operate as well since they are tide together in the same circuit. If you have trouble operating the sunroof along with the alarm acting up, have the siren control module replaced. Volvo will also need to reconfigure the new part to your vehicle or you could still have issues with the alarm. Good luck to you and let us know what happens.