And precisely, that exact webpage tells you the answer you need.
There is no 'ticketing office' located in US. Closest one is YVR.
You'll have to head to your nearest airport's check in counter to do this.
If you look at other countries, ie. HK, China, Australia, France, they will list out their respective office if it exist in that country.

But of course, since you know magic...I'm sure you have other ways