Is is powered on? If yes then try to attend the call on this phone and probably someone will call. Ask them to intimate the owner that the phone is with you. If not then try to contact Koodo customer service and then let them know about the same.
If the phone is on and password locked, you may not be able to call Koodo. Some phones revert to a locked state if left unattended or not used for a certain period of time. In that case, Mayumi's advice is the best course of action.