Shinkansen bullet train during the Olympics

Hello! We are planning a trip to Japan during the Olympics.

We would really like to purchase a JR rail pass. I am worried that if we only book our Shikansen ticket upon arrival in Japan that the Shinkansen will be too busy due to the Olympics. Unfortunately we don't have a lot of flexibility and we need to travel from Kyoto to Tokyo on the morning of July 24. Can I reserve the Shikansen train in advance? or will I only have a chance to book this when we arrive in Osaka on 21 July? Thank you in advance!