The correct spelling is Herrmann after Alexander Herrmann who the move is attributed to by August Roterberg in New Era Card Tricks in 1897. There are some suggestions in an 1896 German magic periodical that Herrmann used the move but didn't invent it. He may have been taught the turnover pass by Johann Hofzinser according to Magic Christian's book NonPlus Ultra. If that is true, maybe it should be called the Hofzinser pass.
If you are flashing, it is because your hand and finger position is wrong. There is a great explanation of how to do it step by step in Volume 4 of Card College. Without a video showing what you are doing, it is difficult to pinpoint what you need to change.