A Waymo Driver can be given clarifications about the world, basically remote human operators can reach into its model of the world, and explain OK, for example, the north side of this road is actually inaccessible, you mustn't drive there. Then, with this improved understanding, the Driver may be able to complete its mission.
They deliberately can't drive the car remotely. If Waymo wants a human to drive the car, they send the human to where the car is, the human gets inside and drives it like any other car.
One easy thing that can go wrong, just as with any other human activity, is the humans make a mistake and their "clarification" is actively unhelpful. If the Waymo Driver is confused about which lane is coned off, and you "help" by telling it the wrong lane, unsurprisingly things will not be improved.
The best solution is always that the Waymo Driver learns how to do better on its own, if you imagine it sees this situation and just confidently picks the correct lane and uses it, Fleet Response never interacts at all, there is no opportunity for them to "provide incorrect guidance". So a bunch of the invisible effort at Waymo is on making the Waymo Driver just get stuff right on its own.