How to Add a Specific (Custom) Enchanted Book to a Loot Table

I am creating an enchantment mod, and there is an specific enchantment called Gravitation that I want to appear in End City chests, with lvl 1 and lvl 2. I don't know how to add this specific enchanted book to a loot table, please help me. (Note: I am using the Loot Modifier Plugin, so I just want to know how to add an specific enchanted book to a loot table.)