If you've had the router for over a year, your carrier (e.g., or Telenor) may provide the unlock code for free. If you'd like to move forward, let me know: is it currently locked to? Do you have your IMEI number Are you seeing a specific error message when you insert a different SIM? Unlock HUAWEI B311s-220 for any sim - DirectUnlocks
On the PCB (near flash chip):