What are the fields in which I can go for a summer internship at IIM Ahmedabad?

You can intern in any of the fields offered by IIM Ahmedabad. Most of the time, the professor won't expect you to be exceptionally knowledgeable in business or finance. Still, you can assist them with a lot of analysis based on statistics, sales, and advertisements.

If writing is your strength, for example, you might search for an internship that also involves editing and literature review. It doesn't really matter what field you work in because all you would be doing is working with written texts.