I would start here: https://www.accessda...on=portal.login
You have to register / make a new account, then I would enter the firm name, address, etc., to search if the FEI number is already in there. I am not certain, but I suspect that since the facility is already registered, they should have an FEI number already.
If it is not there, then I would go to this address (https://www.accessda...tion=common.faq) and go to the "How can I request an FEI?" question. The firm, or whoever is representing them, would need to follow the steps there if an FEI is needed. The FAQ has some information on how the FEI itself is used. There is some information here as well: https://www.fda.gov/media/131911/download.