Xiaomi
Change Carrier Name in Status Bar auf Xiaomi
The carrier name shown in the status bar and on the lock screen normally comes from your SIM card's network registration, but MIUI lets you replace it with any text you choose.
Where the setting lives
The option sits inside the status bar controls rather than the network or SIM settings, which is why many users miss it. Open Settings ➔ Notifications & Control center ➔ Status bar ➔ Edit carrier name.
Setting a custom label
If your device runs dual SIM, MIUI asks you to Choose a SIM card (Dual SIM) first, so each card can carry its own custom name. After picking the slot, use Type a Name and Confirm to save the new label.
What this does and does not change
The change is purely cosmetic. It only affects how the name is displayed in the status bar and on the lock screen, and has no effect on network registration, signal strength, or data connectivity.
If the goal is fixing a wrong or missing network name rather than personalizing it, this setting will not solve underlying SIM registration or carrier profile issues, since those come from the network operator, not from MIUI.