Sometimes, especially during installations, you may not have a LAN cable installed yet. In such situations, you can, for example, share the internet connection of your phone. Here's how to do that.
Be aware that the initial download size might be relatively large (a couple of GB, depending on how outdated your system is).
First of all, unplug the LAN cable on the PC. After that, you can just follow the instructions for your type of Mobile Phone.
Android
Go to Settings and select Connections there
In Connections, go to Mobile Hotspot and Tethering
Connect your phone to one of the USB ports of the computer. Until then the option USB tethering is grayed out.
Once connected, activate USB tethering.
Reboot the PC.
iOS
Go to Settings and select Personal Hotspot there
In Personal Hotspot, enable Allow Others to Join
Connect your phone to one of the USB ports of the computer. A popup on your iPhone appears. Click Trust to enable the connection.
You may need to enter your iPhone passcode afterwards.
Reboot the PC.