The acf/save_post action is detailed here https://www.advancedcustomfields.com/resources/acfsave_post/. You want it to run after ACF saves the data.
In the filter you would loop through the repeater and get the values from the sub fields that you want to search. You would put these values into additional custom fields, not ACF custom fields, just WP custom meta fields, in some type of format that makes them easier to search for your specific needs.
You’re needs are more complicated that I’ve dealt with before and I can’t really say what the best format for the values would be.
