Your question is a bit confusing. If you were served with Form Interrogatories, there is no form for responding. You should answer the questions in order and number your responses to correspondence with the question. Your response should also be on pleading paper and "verified". The language for verification is on the first page of the form interrogatories. You can just copy it. That being said, if default was entered, who served you with interrogatories? What does the motion to set aside default have to do with form interrogatories?
I believe there might be some confusion here. The interrogatories are not really related to the issue of a default. You can respond to the motion to overturn the default and you should have been served a blank form FL320 to use as a response to the motion. The interrogatories however just need to be responded to by the number that they have been listed. You need to sign the response under penalty of perjury. How long ago was the default entered against your ex?