Is this correct to you?

Nope. This is basically relying on the anthropic principle to argue for the existence of God. It assumes that everything popped into being as-is, and that the planet, and life, are unchanging. We know that this is not the case. If the concentration of oxygen was significantly different, then we would have evolved differently to adapt to it, as life constantly did throughout the history of our planet. If the earth was devoid of oxygen, then life would not have arisen, or it would have evolved a significantly different biochemistry to compensate. In essence, it's approaching the problem backwards - that life existed and needed conditions to sustain it, when in reality, certain conditions existed, and life adapted to them.

It's also a poor argument form a logic standpoint, being a cross between a false dichotomy (naturalism vs Islam, with no other possibilities) and a non sequitur (life exists, therefore Islam is true). The first is a problem because there are countless other mutually exclusive religions that believe that their deity created the universe, including Islam, and there's nothing to differentiate between any of them. The second is a problem because there's a huuuuuge gap between arguing that the universe is fine-tuned, and concluding that that proves the accuracy of an entirety of incredibly complex system of religious beliefs.

"Oxygen is only 21% of the air you're breathing. And you're not breathing because oxygen exist. Rather, you're breathing because you need to.. Just saying."

No, that's wrong. We're breathing because oxygen needs to reach all of our cells, and we need carbon dioxide to leave our body.

We breathe because oxygen is easily available in the air - that 21% is more than enough. If we gained oxygen from food instead we'd be eating all day, but we wouldn't need to breathe.

"prove"

Oxygen is only 21% of the air you're breathing. And you're not breathing because oxygen exist. Rather, you're breathing because you need to.. Just saying.

yes that is correct although simplistic. How does this prove God exists?

That doesn't make even the tiniest bit of sense. I might as well say, well, rocks are hard and water is wet, therefore there is no God. There's no logical connection in the argument between the premises and the conclusion.

Life evolves to thrive in the prevailing conditions.

(As proofs of deities go, the argument you quote is hardly one of the best.)