First, did you remove DRM from the azw3 files? If they have DRM, then Calibre cannot edit the azw3 files.
If they're DRM-free already, you have a couple of options.
Save to Disk/Send to Device (can be found in the main toolbar or right-click menu) will update the metadata on the exported ebooks going to the Kindle but does not change the files inside the actual Calibre library.
Embed Metada/Polish Books (not in toolbar/right-click menu by default but you can add a shortcut by going to Preferences - Toolbars & menus) will update the metadata in the files inside the actual Calibre library.
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