To unlock Github access for a given template, you need to purchase that template and to select at least a Developer or a Business license. Github access is granted for lifetime.
Once you've purchased the template, open your account library and click on the item to open the product panel. You can download your purchased product here and request Github access if you have an appropriate license.
After requesting Github access, you are prompted to enter your github username and to select one of your purchased licenses for that product. After that, you're immediately granted access.