[cunning_fish]

Read доверенность as a "letter of attorney" not a "power of attorney"

[sourcery]

Looked it up: доверенность can refer to any of "power of attorney," "letter of attorney," "warrant" or "authorization." Given the context, I think a written letter signed by the passport holder authorizing Ruslan (full legal name, and relationship to passport holder) to take possession of the passport should suffice. It's worth a try. If that's not sufficient, they should explain what they require in greater detail.