When your car is actually in service mode, there's a huge watermark across the screen that says so - it's unavoidable. A tesla service person has to enter a code on the car to put it into and out of service mode. If your car is definitely not in service mode, but the app says it is, there must be some messed up communication somewhere. Try deleting the app and reinstalling a suggested above. Do you have multiple teslas? Maybe one that is in service is confusing the app. And maybe there are more circumstances than we're aware of.