Very easy!!! Just find a mobile phone connected to wifi, connect USB, and turn on USB tethering. At this time, your computer can be temporarily connected to the Internet.
Then open System Settings -> Software & updates. Click on the last Additional Drivers. It will automatically search for some drivers compatible with your computer, check the wireless network card driver Using Broadcom 802.11 Linux STA wireless etc. Select Apply changes.
The last one, click Enable Networking in the status bar, and then click Disable Networking again. This way, the network card can be restarted. Then you can search for the wifi list.