Are you saying that you use this plugin? https://projectdmc.org/plugins/a2z-fedex-shipping/
It does not appear that that plugin generates an email. Is there another plugin you are using to generate the emails? I would imagine what you are looking for is a functionality of that plugin and this FEDEX one working together. After you figure out which plugin generates the emails, you need to ask either that plugin’s author or the author(s) of this fedex plugin how to add the tracking number into an email.
It isn’t a plugin, here is the link to the Ship Manager: https://www.fedex.com/en-us/shipping/ship-manager.html
“FedEx Ship Manager automatically sends tracking numbers to an e-commerce store when a shipment is created. This allows both the store and its customers to track the shipment’s progress”
for the emails, i am using the generic WooCommerce emails. Looking into alternatives, but using the generics for now
I recommend getting in touch with WooCommerce’s support about this via https://woocommerce.com/my-account/contact-support/ if you have any of their paid WooCommerce products or https://projectdmc.org/support/plugin/woocommerce/ if you do not.
i have reached out to them. in the meantime, if anyone else has had this problem id love to know a solution