How should I quit a new job in an amicable way?

Hello all, it has been a week to my new role as an administrator and I hate my new portfolio. Perhaps, due to a misfit of my expectations vs reality, I find myself hating every moment at work. It feels dreadful to go work in the morning. During work, I kept imaging when I can go home. After work, I imagine myself quitting the job. I feel, deep down, I already know I will want to resign in order to protect my mental health long term. The main question is how and when should I approach this issue to my reporting manager? Tell the RM the real reason?

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P.S. I am probably someone going through mid-career crisis.

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