Trigger SimpleLightbox via an External element

I have a WordPress site that utilizes SimpleLightbox to display image galleries in a lightbox - this is currently functional. Now, I need for an external element to also trigger the first image in the gallery. The solution/implementation for this needs to be well-documented, as I need to apply it to several other templates on the site as well. Note that this implementation should not use the SimpleLightbox WordPress plugin or any other additional plugins.

SimpleLightbox documentation: https://simplelightbox.com/
Project Overview: https://www.loom.com/share/f480dcb318b54ce7925bbe5f2b02d962