This needs to be done using either an acf/save_post filter https://www.advancedcustomfields.com/resources/acf-save_post/ or an acf/pre_save_post filter https://www.advancedcustomfields.com/resources/acf-pre_save_post/
In either case, in your filter you get the field and use wp_update_post() to update the title of the post https://codex.wordpress.org/Function_Reference/wp_update_post
There is an example of using acf/save_post here https://support.advancedcustomfields.com/forums/topic/set-post-title-from-field-group-toggle/ and you can probably find others
