For your plugin question, you need to contact the plugin’s support guys. Plugin questions are not within scope here.
For information about templates, start here to gain knowledge on how they work: https://codex.wordpress.org/Templates. Templates are part of the theme, so to change the template, you have to change the template used by the theme.
But you don’t want to change theme templates, you want to create a Child Theme that uses your current theme. Put your modified templates in the Child Theme, so any theme updates don’t bork your custom templated.
Learn about Child Themes here: https://codex.wordpress.org/Child_Themes .