Advance Seat Reservation

Hello. Konichiwa.

First question: We purchased our Green JR Pass while still in the US and we have received the vouchers already. We have not activated the vouchers yet since we are still in the US. We have read and seen in multiple channels that it is advisable to reserve our seats in advance. How can we reserve our seats online before arriving in Japan?

Second question: If we can not reserve seats before activating the JR Pass, can we get assistance at the JR Pass ticket office at Narita airport in reserving our seats?

Thank you. Arigato gozaimasu.

Liza