Effectively the "sonship" or Kingdom God created, is really a kind of "collective consciousness". Yes it's not what ACIM would officially refer to as consciousness, having nothing to do with perception etc, but we do SHARE mind. There is this one mind which houses many minds. It's similar to the Borg on Star Trek in that sense. Everyone is plugged into everyone, and indeed also acts "as one" in a giant collaborative way.
This also means that you are not just some separate chunk of the collective. Whereby other people are separate chunks, as if there are then wires connecting you together. But moreso you actually are everywhere and in everyone. And your brother IS part of you literally. You share your actual self with their self so fully they are basically one, yet two. You really are the whole collective, and are also part of it. The whole, and the part, as in a hologram.
What we call ego or separation, is what you get when you take someone who is part of AND all of this collective, and you try to "fence them off". To isolate them in a little prison with a wall around it, so that you can sort of say, this collective unit is now divorced from the collective, disconnected from the "hive mind", isn't sharing anything, can't "hear" the thoughts of the other brothers any more, and has now become "alone" or orphaned.
This self which was, and still is, part of the whole, sees itself as lacking the sense of relationship and sharing that unites it with the "rest" of the collective, which is also the rest of itself. And so it is kind of like a split off part of the whole, which was part of the whole, but has forgotten that it was whole. So now it sees itself as only a part, and only partial. Such a sense of identity is alone and lonely, isolated and like on a desert island, cut off and unable to relate or share.
To "undo the ego" is really a matter of reintegrating the rest of yourself, which means plugging yourself back into the whole sonship, to share everything with everyone, to have real relationship with all equally. That is really just a matter of taking away the separations - the walls - that seemed to imprison that part of the mind, so that that part of the mind is able to reconnect and integrate with the whole again.
We're not here in the business of exterminating parts of mind, we're actually in the business of setting them free from imprisonment. An imprisoned mind acts like an ego because it has limited itself. But when that same mind lets go its sense of selfishness, specialness, or exclusivity, it expands to return to the whole mind. This isn't really a destruction of your self, it's just a removal of the sense of separation which gave you a false sense of being small and limited.
In that sense, the part of your mind that believes it is an ego, lifts itself away from the "egotism" that imprisons it, the walls are transcended, the sense of self expands to be more inclusive, you become more than "just yourself", and all of this sense of isolation, loneliness, abandonment, fear, hiding, darkness, being trapped, being lost, etc, all that stuff goes, because the mind opens up to freedom and joining again.
You are returning to the family of God. The chains that bind you and keep you in a hellish prison are what need to be undone, not your "self". But while you live in the chains, you will see yourself as small and selfish because of what the chains imply about you. If you identify with the prison you become the prisoner. But you are more than the prison, you are only imprisoned by it if you give it the power to do so. The ego is a prison cell, not a self. It's like a trap that you've become stuck in, and all you need is to be set free.