how to claim VAT refund on apple products while coming back from USA

You will have to find an Apple Store that offers that service and ask them. You may have to find one in a big city such as New York since I doubt it is available at most stores. I have not seen anything about it online.

If you are traveling by air, there is an area at the airport that handles VAT refunds. Make sure that you have your sales receipt, etc.

This area is usually crowded, so allow for extra time for the process. My experience has been that probably half of the people who are eligible for the refund don't bother with this when they see how long it might take.

The sales tax structure in the U.S. is VERY segmented; with the tax collections made at any store going to State, County, and Municipal taxing authorities. (or any combo of the three).

There is no “National Level” collection.

Hence there is not one “authority” from whom to request a refund.

As pointed out by Limnos; unless a particular Apple Store provided this “extra service” at purchase, I suspect your odds of obtaining any refund are near-zero.

Consult a tax specialist in your country.