Once you have created one or more subitem templates, you can then apply them easily to main task items in your board.
Step 1: To get started, click on the Updates icon next to your main task item:
Step 2: Once in the Updates section, select the Subitem Templates app to open the app, and you will be able to choose the subitem template you need from the dropdown of templates created:
Step 3: Select Add Subitems after choosing which template you would like to apply:
The subitems will be applied to your main task item:
Important Note: If a subitem template is applied to a main task item which already contains subitems, the template will simply be applied to the bottom of the existing subitems. Here is an example...
Existing subitems with template applied: