To login to your AT&T router, you can follow these general steps:

Connect your computer or device to the AT&T router using an Ethernet cable or through a Wi-Fi connection.
Open a web browser on your device.
In the address bar of the browser, type in the default gateway IP address for AT&T routers. This is usually "192.168.1.254" or "192.168.0.1". Press Enter.
This should take you to the AT&T router's login page.
On the login page, enter the default username and password for your AT&T router. These credentials can usually be found on a sticker on the router itself or in the documentation that came with the router. If you have customized your router's login credentials, enter those instead.
Click on the "Login" or "Submit" button to proceed.
After successful authentication, you should have access to the router's administration interface where you can configure various settings, such as network name (SSID), Wi-Fi password, security settings, and more.
Please note that the exact steps and default login credentials may vary depending on the specific model of your AT&T router. If you are unable to log in or have forgotten your login details, you may need to reset the router to its factory settings by pressing and holding the reset button on the router for about 10 seconds. However, be aware that doing so will erase any customized settings you have made, and you will need to reconfigure your router from scratch.