Theme that includes a “core” plugin but the files in theme and child folder ignored

I have purchased to themes from Qode which my client has chosen.

Both themes have a “core” plugin which is used for specific areas, like “events”, breadcrumbs and portfolios” etc.

Firstly, annoyingly the theme does not support breadcrumbs for custom post types so I needed to change the file that displays these, which I have done via the core plugin fine, but I am aware that during an update this will probably get overridden.

I have tried to save the file I edited within both the main theme and child theme in the same hierarchy as the plugin but still the plugin files are the ones used – not the ones in either the theme or child folders.

How do I get the site to use the files for the plugin that are now stored within the theme or even better, the child theme?

Never had this issue before so really stumped – any help appreciated!

Thanks in advance