You have lost an item in an Taxi. If your order was pre order then you have all the information about your driver and you can contact the driver by phone. If this is not the case the hope for finding it back is indeed small.
Uber = use the uber app and call your driver. you get connected to your last Uber or send an email selecting the trip, use help and send an email.
You have all the information from the organisation and or the driver you orderd your Taxi. Call your driver using that information.
If you have no information regarding your driver, licence plate nr or organisation name your last chance may be: I Lost