This is a Library Management topic <Moved>. Editor is for Inside a Book
You used the correct words:
Bulk Metadata Edit
Select Books: Tap 'E"
Because you selected multiple books, you are in Bulk mode
Bulk mode has a Search and Replace tab, where you can do Bulk editing of the metadata.
(Simple Metadata changes can be done from the main tab, just like would be done in Single mode)
Now the Caution - Tip
IMHO don't mangle a standard field like Title, Author
Those are used to do many things in their proper format
If you need/want additional data when transferring to devices, use the (device driver) Template or Plugboard. This leaves the Library data pristine