How to update Xcode using software update if the App Store is not accessible or download?

There is a related question, "How to download Xcode 13 if the App Store is not accessible?" But if you already have XCode installed and run the following command:

xcode-select --install

The following message appears:

xcode-select: error: command line tools are already installed, use "Software Update" in System Settings to install updates

What is the command to update XCode via the command line or by download? I know the following basic commands: **List all updates:**

softwareupdate -l

**To install a specific update** in the list, use the following format, but replacing NAME with the update's identifier:

softwareupdate -i NAME

softwareupdate --install 'macOS High Sierra 10.13.3 Supplemental Update-'

**To install all available updates** for your system type the command:

softwareupdate -i -a

But I don't see one for XCode:

Software Update Tool

Finding available software
No new software available.