Answer:
Make it sincere but not too sincere. Be specific. Explain what happened. Be honest.
Step-by-step explanation:
Dear Mr/Mrs....
I hope you are doing well. My notebook has gone missing. I... (explain what happened and how you lost the notebook) When I went to get my notebook, I could not find it. Hence, I am not able to... (do what you need to do). Thank you in advance,
Yours truly,
(Your name)