I'm using fullcalendar and I need to let user select multiple rows for create a multi-resource event (documentation) but I not find how to do so. Anyone have any idea?
I'd say it's not supported. https://fullcalendar.io/docs/selection/select_callback/ indicates that when a selection is made, the callback will return a single "resource" object which will indicate the resource chosen by the user. This implies that selecting multiple resources via dragging the mouse on the timeline is not possible.
You can create events via the "events" feeds which are associated with multiple resources (see https://fullcalendar.io/docs/resource_data/associating_events/) but it's not supported via the UI yet.
You'd have to create your own UI to allow the user to specify this, and/or put in a feature request to the maintainer to add this support in future (it may already be on the roadmap, I haven't looked).