Hi @Sue_Milford and welcome to the forum!
It’s not currently possible in native Asana to automatically have a set of subtasks attached to a form submission. However, it is possible in my Flowsana integration - there is a rule action specifically built for this purpose. You can see more about it under “Add Subtasks from a Template” in this forum post.
You can use this “Create subtasks” rule action in conjunction with form submissions in several ways. In the simplest case, you can have the same set of subtasks created for every instance of a form’s submission by triggering the rule action on the condition of “When a new task is created”. You can also build a more flexible scenario where a different set of subtasks is added depending on a value the submitter selects in a form field; for example you could have different categories of maintenance requests, each of which generates a different set of subtasks to be created. You’d accomplish that by mapping the form field to a custom field, and then building a rule condition based on that custom field’s value.