Navigate to the side navigation bar and choose "Customers" from customers.

Select the particular customer you wish to add Billing Template.

Scroll down the right-hand window to find the "Billing & Contract" tab and click on it.

Choose the "Billing & Invoice" tab from the provided tabs.

You'll find a button on the right side of the billing template, allowing user to select the default template.

When clicking on the dropdown menu, users can view all available templates along with a preview. From there, they can select the appropriate template to set as the default option for that customer.