The business name field is greyed out because a business name cannot be changed once it has been added to your account. Your USPS Form 1583 for that business has already been notarized, and the name on file has to match the notarized form.
If you need the business listed under a different name, reach out to us and we can remove that business from your account. You can then add the new business in its place.
Keep in mind that adding a business requires notarizing a new USPS Form 1583 for it. You can find the steps here: How do I add a business (or additional business) to my existing account?