Premise 1.

Humans have consciousness and they are aware of it.

This premise is trivial. The fact we are aware of our consciouness may or may not be what consciousness is, but this is beyond what the present argument addresses.

Premise 2.

Given premise 1, the knowledge we are conscient beings is encoded in the brain in some way.

This could not be otherwise, since the opposite would suggest we know something that is not present in our brain. This could not be the case, as neuroscience suggests.

Premise 3. Premise 2 requires consciousness to exist and additionally to act upon the brain.

This could also not be otherwise, since the opposite would suggest that the brain knows something without interacting with it. Note that this does not imply that anything we think exists beyond of our minds. For example, assuming antirealism on mathematics (numbers being only a notion in our minds) is true, numbers, i.e. the notion of them, do act on our brain, e.g. thinking 1 plus 1, leads you to think 2. To summarize, premise 3 does not state anythink about the nature of consciousness. It only states that it acts upon the brain, either as a mere notion in the mind or something totally different.

Conclution.

Therefore, consciousness acts upon matter, at least in the case of human brain.