We have these two SharePoint lists, "List 1" contains a comma-separated "list" of tags, say "tag 1, tag 2, tag 3" etc.

In the Nintex Form for "List 2", we have a list lookup which we want to populate with items from "List 1" based on whether the tag column from "List 1" contains a certain tag.  

This cannot be done out of the box using Nintex Forms as the List Lookup filter seems to only work in a "Equals" sense.

I'm happy to use JavaScript for this but any pointers with how to start this off would be greatly appreciated, as my JS is not perfect.

Thanks