They usually sell the Yikatong at the subway ticket windows. They have them for sure at the Airport Express ticket counter. Reloading the card is easy and takes a few seconds in any subway stop. Follow the simple instructions on the screen.
The issue is getting a refund for the balance. It can only be done in a few places (and the airport is not one of them). Whatever time you gain by not having to buy tickets every time that you ride the subway, it offset by a multiple in the time wasted to get the refund.
in my opinion, getting the card is not worth it. It's not like Shanghai where you can get a tourist card for unlimited travel for a few days.
Best is to run your card down to zero value.