If you would like to authorize someone to collect the keys on your behalf, here is a sample template you can use to write an authorization letter for key collection.
I am, [Name], the registered owner of the undersigned property. This letter is regarding my inability to collect the keys to the property by myself. This is why I am formally authorizing my [relation], [Person’s Name] to collect the keys on my behalf.
In my absence, [he/she] shall complete all the necessary documentation and signing procedures. I request you to observe [his/her] actions of equivalent authority as of mine until further notice. Kindly take note and hand over the keys to [him/her] after verification of [his/her] identity proof. Also, in case of further clarification, feel free to contact me at [Phone no.].