How to request for a bin check?

I received messages from two buyers saying that they have been sent a product that is the older version of the product on the listing. I have been selling this product for months and this is the first time someone raise an issue like that. I am doing FBA and using a prep center to send the product to Amazon. May I ask how to request a bin check to see if those two units are the only products in error?

Thank you.