Locate the Glossary Object in your library. This object is usually found in the Common Content > Front and Back Matter folder.
Alternatively, you can search for it using the Object Type filter, shown in the search example. You will probably get results similar to those shown. Ignore the objects with Template in the name; you want the Glossary Object.
Because you'll need to add this to your book, locate which folder it is in: Right-click the object, and from the context menu, select.