Microsoft isn’t pulling that airline name from “their side.” Outlook Calendar reads airline data from the external flight-info provider (IATA codes + flight-data feed).
If 4I → Air Antilles is showing as IZAIR, that means the flight-data provider has the wrong mapping, not Outlook.
You can’t fix it from your end. Microsoft also won’t manually edit it. You must report it through:
Help → Feedback → “Flight info incorrect” inside Outlook.
Microsoft forwards it to their data provider, and that’s the only way it gets corrected.