What do you mean that it exists? Do you think it is a concept, or an actual entity, or what? What do you mean when you say it exists?
Define what you mean by exists? Is it a concept like “justice” or is it physical, or is it supernatural, or what?
Justice is about moral (we are not yet at this stage)
physical usually imply unconsciousness (so it is certainly not that, at least not at this stage)
supernatural imply that it is over or more than nature, I don't even know what does it means (so I won't use this term)
existence is relative to reality. To say that something exist is to say that it is in reality, or that it is reality itself. Reality I defined it at what is behind our perceptions (or more adequately what generate them).
consciousness as I told you so many times, is what make able the apparency of perceptions. It is what makes perceptions possible.
About god, I simply used it as another term for consciousness. god is a indeed word used by many theist to refer to consciousness. You do not need to agree but disagreeing it is like disagreeing that when French use the word "chien" it refera to "dog" in English.
Anyway, let's continue with the word "consciousness" to keep you psychologically safe.
Why you keep saying that I do not refers to the same thing as what you think is consciousness?
You feel something, you feel yourself, you experience emotions, you see bananas, dogs... all this are perceptions, they are in some sense inside (or part of) consciousness
so consciousness is what contains these perceptions but it is also what generate them because without consciousness there will be no perceptions
the definition is of course not precise because we don't want to make assumption yet. I want to give possibilities of explanation.
for example, maybe as you said it is physical (generated by brain processes) but at this stage we cannot say that. we doubted everything and we are left with consciousness that in some way makes perceptions possible.
I think you have also consciousness so you can also help me build the definition instead of just saying that I do not define it.