Go ahead and collect emails from your project supervisor, team leads and peers about your tenure, project details, technical expertise required for the project along with their contact details (email and phone numbers) and send the below covering letter to USCIS. You should be good to go.
This letter is in support of the query raised by USCIS.
Please be advised that since the policy of the “Human Resources department” in the company I worked does not reveal the details of the project I worked, you are welcome to reach out to the personal at “Human Resources department” for details if any.
I am enclosing photocopies of letters supporting my experience from the project managers & peers to certify my tenure, project details along with technical expertise & experience via their corporate emails with all their details of designation and their contact phone numbers. Hence, we request you to consider the emails and their content for your verification needs.