Firstly go to Side Menu > Settings > WA Message Templates.
Before you can use the template you need to activate by click on the top right button.
After that, you can make a change to your template.
At your order detail
Firstly add your message at delivery update message at order detail, and click 'Update Message'.
After that, you may want to send a message to your customer with pre-setup template.
By clicking at WhatsApp button, you now have option to send with template: 'Order Update'.
It's essentially send a message to your customer with predefined text and with the link to your customer order link.