If you are unable to collect your passport yourself, here is a sample template you can use to write an authorization letter for a passport.
This letter is to bring to your attention that I, [Your Name], [Passport Number] will be unable to collect my passport. This is why, I hereby authorize my [relation], [Person’s Name] to receive it on my behalf. I provided [him/her] with the passport invoice and other essential documents for verification purposes.
Also, I have asked [him/her] to carry 2 identity proofs which can help you authenticate the recipient’s identity. I request you to cooperate with the same and to hand over the passport results to the mentioned applicant. For further clarification, kindly contact me at [Phone No.].