Linking IC card to Shinkansen e-ticket

My question is regarding online purchase of Shinkansen e-ticket (via eki-net.com) if I already have IC Card (Kitaka).
How do I link my IC Card to the purchased e-ticket? I tried searching for the answer and even tried to do a reservation but proceeded up till payment page. I can't continue since my travel date is too far ahead. Will be traveling on Hokuriku Shinkansen between Tokyo and Iiyama Stations towards the end of March.

There is a screen towards the end of the process (after payment), which allows you to associate IC cards with the tickets.

Thanks Uji!