How to Assign Template to Site from Custom Fields menu on the Site?

Pre-requisite

Step 1:

Navigate to the Site where you want to assign the template to.

On the menu, click on the Custom Fields menu item.

Step 2:

Then Click on the drop down as shown below and select the Custom Field Template to apply.

Click on the Add to Site button to add the template.

Once added, it will show as below.