The paragraph you quoted is saying that a map can't have a subregion that depicts the entire map in perfect detail, because this would require an infinite sequence of smaller and smaller maps-of-maps.

One solution to this is to make the sub-map incomplete, e.g., only depict the source code. Alternatively, an AI can build an external replica of itself in perfect detail; but the replica isn't a component of the AI (hence doesn't lead to a regress). An external replica can be used as a sort of map, but it's not a representation inside the agent. It's more like a cheat sheet than like a belief or perception. In many cases it will be more efficient for the agent to just look at a component of itself than to build a copy and look at the copy's components.