Help adding Category to custom post type

So i recently purchased the theme “We Rock”. I have tried reaching out to them for support, but they haven’t responded and my client needs immediate help.

Within the theme there is a custom post type that is set up for events. I have successfully created the function within the custom post type to allow for the creation and association of categories.

Now, the problem. There are widgets that were created in page builder for custom events. I want to add a section within the widget so that i can define or pick one of the categories so that the widget only displays the events within that category.

Can someone help me figure out how to add that option within the widget?