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I'd like to confirm my reservation.
Literal
Reservation-of confirmation [object-を] do-want-[explanatory-のですが].
Standard hotel-counter polite request: 確認 ('confirmation') + the soft opener ~たいのですが invites the staff to take the next step without an outright command. Contrast with 再確認 (reconfirmation), which adds the prefix 再 ('re-') for already-existing reservations being checked again.