Where to activate JR pass in Fujiyoshida

We have purchased 2 week JR passes. We arrive at Narita on August 30 and leave on September 14. We plan to use the passes to travel from Fujiyoshida to Kyoto and back on the shinkansen. Then possibly use the passes to return to Narita on the 14th. We probably won't take the NEX to Shinjuku to catch the Expressway Bus, for which we have a reservation, because we don't know how to get from the NEX train to the Expressway Bus Terminal. And we don't want to use the JR passes when we arrive and not have them for the return to Narita. We won't have time to activate the JR passes at Narita. So where can we activate them in Fujiyoshida?