A：1. First, ensure the SIM card is in good working order: undamaged, with no severe oxidation on the metal surface, not suspended due to unpaid bills, and correctly positioned in the SIM card tray.
2. Check if airplane mode is enabled on your phone (please disable it). Then, compare the signal strength of phones using the same carrier's SIM card to confirm network coverage in your location. (You can also test with the same SIM card in different phones.)
3. If the lack of network signal or inability to access the network is caused by installing certain software, uninstall the software and restart your phone.
4. Compare the parameters of a working SIM card from the same carrier, manually adjust the phone's APN parameters, and enable VoLTE. APN settings: Settings - SIM & Data Management - Mobile Network - Access Point Names - Select the "+" sign to add relevant parameters; VoLTE enable: Settings - SIM & Data Management - Mobile Network - VoLTE - Enable, select the highest preferred network type.
5. If there is still no network, provide your IMEI to the carrier to inquire if the phone is locked and if it can be unlocked. (If it is locked and cannot be unlocked, you will have to replace the phone)
6. If the problem is still not resolved after the above troubleshooting, please provide a video of the malfunction. The phone's radio frequency module may be faulty and needs to be returned for repair.