The proper apology entails the words explicitly indicating wrong has been done, no justification, and a plan to remedy the whatever. The good news is that there is now a short book - 100 pages - which makes all that clear, in simple concepts and language.
The book is "I'm Sorry: The Art of Apology & The Gift of Forgiveness." It's published by Hartherleigh. Here you can read more about it on Amazon.com.
In addition to guiding your clients through the apology process, the book provides insight on why human being tend to get themselves into the kinds of pickles which demand apologies. Therefore, those who absorb that can prevent a lot of the transgressions which end everything from enjoying freedom and not being a guest of the state to prospering on a career path.