The warning triangle indicates an existing fault, and information about this is displayed in the panel between the main instruments. If the message you are receiving is 'Only leave vehicle in position P', this could be indicating that you should leave the vehicle in Park when switching off if you are not already doing so, or it could indicate a fault with the gearbox itself - potentially an issue with the gearlever position sensor. If this fault occurs every time you use the vehicle, we would suggest having a diagnostic check at an independent SEAT/VW Group garage.