Need help with sending emails

I am using another plugin that notifies users when a product is back in stock by sending an email. Using your plugin it’s not triggering this plugin to send emails. I contacted them and they asked for the developers of this plugin to look at this code:

https://github.com/wcmarketplace/woocommerce-product-stock-alert/blob/master/classes/class-woo-product-stock-alert-action.php

What code would I put in the functions.php file?

Would it be an add_action command? I’m not too familiar with PHP code.