What is the level 6 token and combining tokens thing???

It says "get an S- or higher to earn master level 6 token. Combine tokens to advance further..." Ok, well I have several champs that I got to level 5 with and earned an S+ with...now what? wtf? Where do I go? How do I "combine" them? Where's the level 6 and 7 icon? What? I don't see anything in the essence store that says "icons" or anything remotely like that.