strapi.query('model', 'plugin').action()
https://strapi.io/documentation/developer-docs/latest/concepts/queries.html#custom-queries
You can also hook into the ORM (Bookshelf/Mongoose) using the .model action
So something like strapi.query('user', 'users-permissions').model.someMethod
Note that if the model is in the root API folder, there is no plugin, so it’s just strapi.query('model').action()