Unknown device notification -can't disable

My daughter received and unknown device notification through her tiny my iPhone app -it shows that it has been tracking her for the last 2 days and seems to also notify her when when this device is turned on. periodically to track her car. When she hits continue and then disable it will not let her disable this unknown device. It is clearly an air tag that someone has attached to her car to track her , stalk her etc. She has contacted the police and we are trying to find someone with a bug detector as we have not been able to find the air tag or device on her car so far. I am wondering why we are unable to disable the device though - Shouldn't there be a way to do this if the device is illegally tracking her ? What other possible way is there do disable this illegal device if we cannot find it?