Here is the definitive guide to doing it correctly. Warning: A hard reset will erase everything you have configured. You will need to set up your internet connection (PPPoE, Dynamic IP, etc.) and WiFi password from scratch.
A paperclip, a SIM ejector tool, or a thin pen. How to Hard Reset XIAOMI Mi WiFi Router 4C
Find the Hole On the far right side of the port panel (usually next to the power port), there is a small, recessed hole labeled Reset . Here is the definitive guide to doing it correctly
Make sure you have your ISP login credentials handy before proceeding. This is the most reliable method, especially if you cannot log into the router’s web interface. a SIM ejector tool