Simple Wordpress Auto-Assign Category Plugin

I need a plugin where I can auto-assign sub-categories to Posts when the Post Content has the "Sub-Category Name" found in the Post Content. Basically, I want to target a specific Main Category i.e. Manufacturers which may have 100 different manufacturers as sub-categories. The function will loop all posts and then for each post it will loop all sub-categories for the selected Main Category. If the sub-category name is found in the post content then add that sub-category to the post.