Books you create yourself using BookBuilder can be installed by simply copying them into the folder where PocketBible stores its books. PocketBible stores its books in:
~/Library/Application Support/com.laridian.PocketBible/Laridian Books
To get to this folder, select the Go menu in Finder. Hold down the Option key to reveal Library in the menu, which is usually hidden. Select Library and click your way down to the Laridian Books folder. Paste your LBK file into this folder. If PocketBible is running at the time, you’ll need to close PocketBible and re-launch it in order for it to see your book.