Do not assume it's an envelope if it says "envelope", it could be a box
If you are still unable to locate the package, follow directions below
Select the "?" in the upper right corner
Select "Return Items"
Select "Package Missing"
Select the correct TBA123456789 that is actually missing (be very careful to mark the correct package that's missing)
Select "Continue Delivery", if you have more packages to deliver to that location
Select "Swipe to Finish" if that's the only package for that location.
If/when you find the package later, determine how far the location is from you, and either Reattempt Delivery, or CALL Dispatch to assist in making the decision.
If it was determined to be too far to backtrack at the end of your route, make sure you add it to your self debrief as this will remove it from your custody.