You can override TownHub Add-Ons plugin template from child theme by copy .php files to child-theme/cth_listing/ folder.
For example, you want to change user login/register modal. Which get content from townhub-add-ons/template-parts/shortcodes/login-modal.php file. So you have to copy login-modal.php file into your /cth_listing/template-parts/shortcodes/ folder in your child theme to edit.
