I’m not sure about a plugin, but you can definitely add custom meta that allows you to set the event date, or even an event daterange (my preferred way of handling this is an event date and a duration, cuts down on calculations in the backend and is generally easier to understand, but ymmv). This allows you to keep your post dates in order while maintaining event dates, and also allows you to query by either of them using WP_Query, should you have that need.
