Unlike simply rebooting the router (turning it off and on), a hard reset wipes all your custom settings—WiFi name, password, port forwarding rules, and parental controls—returning the device to its "out of the box" state.
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. How to Hard Reset XIAOMI Mi WiFi Router 4C
A paperclip, a SIM ejector tool, or a thin pen. Unlike simply rebooting the router (turning it off
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. port forwarding rules