Possibly in the videos ==>>
Video Tutorials
Ctrl+A is a 'standard sequence' for select all, and Edit metadata in Bulk is an option in the Edit Metadata button drop down.
Aside : The late Larry Tesler 'invented' Ctrl+A/C/V/X/Z etc when he was at Xerox working on the original WIMP user interface design - we owe him a lot. He died a few weeks ago.
BR