There is a bit of a procedure for the first time (and then its straight forward after that)
You can goto the Bazaar module page and click on the DnD Beyond filter.
Then click refresh. All the books will appear.
You also need the forge compendium browser module installed
Finally you will need to follow the instructions in “important information”. This explains how to add a browser extension to chrome in order for it to work.
If you need further assistance, its probably a little easier on the Forge discord page.