Android
Select a Mobile Network Manually auf Android
Android normally scans for available networks and connects to whichever one offers the strongest signal or matches your home carrier agreements. This automatic behavior is convenient in everyday use, but it can pick a network you don't actually want, especially near borders, on cruise ships, or in buildings where a weaker carrier has better indoor coverage.
Manual selection bypasses that logic. You see every network your SIM can reach and connect to a specific one yourself, which is useful for testing coverage, avoiding expensive roaming partners, or forcing a connection to a carrier you know performs better in your location.
To switch to manual mode, go to Tap on Settings ➔ Tap on Network & internet ➔ Tap on SIMs. On a Dual SIM device, tap Choose a SIM card (Dual SIM) first to pick which line you want to configure. Then turn off Automatically select network and use Choose a Network to pick from the list that appears.
Keep in mind that a manually chosen network stays fixed even if you leave its coverage area, so calls and data can drop until you switch back to automatic mode or pick a new network by hand. For daily use in your home area, automatic selection is almost always the better default.