Auto Generate Custom Post Title in Wordpress theme

We have a wordpress website with the point finder classified theme installed (Themerforest - Point Finder - Directory WordPress Theme) The theme functions great and was the best of several that we tested. But, now we want to make some customizations that are not available in the theme. We would like to automatically generate a title for the custom post type that the theme creates when a classified is input by the user upload of ads. The post title would generate from the custom post type and 2 custom fields that the input form collects. Hopefully we could do this with a function in the child theme that wouldn’t cause us to need to customize the main theme file (so theme updates can still be taken advantage of). I have seen some examples of this done successfully in other input forms but have been unable to implement myself. There is also a wordpress plugin that we might be able to customize that would do the trick: Auto Generate Title (available in the wordpress plugin depository) We have tested the plugin and I works flawlessly on regular posts to create a title based on the first few words in the page content. We will also use this job evaluation for some additional changes (less urgent) that we would like to do to the site.