I DM & am running the Shattered Obelisk campaign for my group. We play long distance and utilize the Maps feature.  I go off script fairly often, as I like to encourage the players to make their own choices. They encountered a Spectator and instead of battling, they opted to talk. After a few successful checks of the dice, they now have him as a companion. Specifically, the wizard in the party has the “controls”. is there a way to give him full access & control of the spectators stat block? Or will the wizard need to tell me what the action is and I roll etc. 

Its an ingame feature to have a gazer familiar, so why not a spectator!-

You honestly dont even need to nerf their statblock if your party are at least level 5 or so; they typically flee instead of fighting so you could have the friendly spectator follow the wizard simply to study their magic. In return it offers to guard them by flinging a few eye beams at whatever attacks the party while at a safe distance. I would say give the wizard access to its statblock, however you would still be in control of where it is positioned, its behavior, etc