I had the same question. I tried to go into admin and I don't see an option to enable/diasble calednar access to exisitng users. This role feature might come out in August 22nd release, and we might be able to assign calendar role after that. Lets wait for an official answer from Marketo, I am just speculating here.
Hi Martin, Harjot, and Venus, the feature will be available after the next release as Harjot suggested. Once the new version is released, you'll be able to assign the 5 licenses to the appropriate users.