For the ASUS S400CA series, you can check your model name in the BIOS settings, and then download the corresponding BIOS file. The steps are as follows:

1. Press F2 during boot to enter the BIOS setup interface.

　2. Then press F12, please pay attention to the lower right corner of the screen, the name of this model will be displayed. Please follow the model name to download the BIOS file with the same name from the ASUS official website.