Take the iPhone 12 as an example, its system is ios 14, want to use the mobile phone to connect to the router, you can first open the mobile phone browser, enter the router's default iP address in the address bar, generally 192.168.1.1;
After entering the configuration page of the router, click the icon in the upper right corner of the page, you can see the basic configuration page of the router.
Click on Wireless Settings, select the WiFi name and password, save and exit.