How to quit amicably?

Greetings everyone, it has now been a week since I started my new position as an administrator, but unfortunately, I am not enjoying my new role. I believe this may be due to a misalignment between my expectations and the reality of the job, which is making every moment at work dreadful. I find myself constantly thinking about leaving and protecting my long-term mental health. As someone going through a mid-career crisis, I am unsure of how and when to bring this issue up with my reporting manager, and whether or not to disclose the real reason for my dissatisfaction.