Brewquets stock notification is currently manual as products do not tend to sell out like on Beer Cartel.
This is done natively within the Language setting of Shopify using a contact form but in future it could be possible to use an automated notify app for out of stock items.
To amend the text of the notification section go to Edit Theme > Locales Folder > en.default.json
Then search for "unavailable" to find the unavailable / out of stock section.
"sold_out": "Sold Out"
"description": "Enter your email to be notified when this item is back in stock"
There are two text types that we use.
"Sold Out"
"Enter your email to be notified when this item is back in stock."
or
"Enquire Now"
"Send an enquiry regarding this product."
The "Enquire Now" and "Send an enquiry regarding this product." was being used to allow for the custom corporate boxes to not show "sold out" but note this will be done for all products if it is changed to this.