We can’t even alter Earth’s atmosphere to make it more suitable or to stop global warming, what to speak of Mars.
Sadly, the idea of terraforming Mars is mostly science fiction, not real. Mars is a dead planet. Even if we could somehow get a breathable atmosphere there, because there is no organized magnetic field it would blow away and there would never be protection against dangerous UV light from the sun.
Mars is not inhabitable for long-term human presence.