High b flat is just like low b flat..For fingering anyway. If you need to trill it, you use the thumb key. But I may have misunderstood your question..
The best fingering for top B-flat is the left hand thumb, plus your index finger on your right hand and the first trill key (your index and middle finger will probably be touching each other.) Do not use the index finger on your left hand (or any other left hand finger other than your thumb.) It is preferable to leave off your right hand pinkey is well, but this is not crucial.