I recommend you don't over-do the session. That is, don't make it to long and teach what the audience needs to know. Break it into parts if needed, covering the more troublesome areas first.
If you are using PowerPoint, add some audio and video clips that help emphasize the subject matter. Use scanned images of forms that were wrong, and explain why, but without pointing fingers.
Tell them of real examples in your bank and others, driving home your point with discussion of penalties, poor service, time spent on corrective actions, etc.
And don't speak like Ferris Bueler's teacher, Ben Stein. Change your inflection, throw out some humor once in awhile and grab their interest, as best you can.
After the session, distribute a form asking them what could have made it better, constructive criticism only.