As always in an interview, a question is not as simple as it sounds. If you went for a simple “yes” or “I have completed the form” as an answer, they might surprise you with a practical test of your skills. They might hand you a form together with a medical record and ask you to complete the form.
Therefore, if you have never done it before, I suggest you to say the following:
I have never completed an insurance form before. However, I believe I can learn to do it quickly, since I have experience with completing other forms.
What to answer if you have experience?
If you have an experience with completing insurance forms, you should speak nicely about the experience, and say when you learned to do it.
I have completed dozens of insurance forms. I can do it without an assistance. I learned to do it during my medical assistant certification course.