This is a built-in feature. You can Shift-Click to select multiple events and then drag them to a new date, time, or resource.
Productivity and Shortcuts
Option-Drag to Duplicate Events
This is a built-in feature. Hold down the option key (Mac) or the control key (Windows) while dragging an event to duplicate it.
Automatically Open Links in Event Description or Location
Example code for adding a button to scan an event description or event location, and open the first URL that is found in a new browser window.
Remove Attendees when Duplicating Google Calendar Events
When using Drag and Drop to duplicate an event, this event action will remove the attendees on the newly created events.
Select Related Events Automatically – Smart Multi-Select
An example custom version of Multi-Select that selects items with the same contact, resource, or any other custom filters criteria that you specify.