Go to a social security office while your green card is still valid, and ask for a new SSN card. They will then give you a new one that doesn't have those restrictions, which you can then provide it to your employer if asked, together with a driver's license or other form of state ID.
Alternatively, you can go on the social security website, and request a new SSN card online. You will then visit your local office after doing that, make sure to bring your green card with you when doing so, and you will get a new and unrestricted SSN card.