I need to get the part tha cover the metal

Thanks for posting. We may be able to help, but I need to see the entire operator to confirm what kind of cover might work for you. By the entire operator, I mean also the link arm(s) that jut out the back of that base and connect to the window sash, helping pull and push it. A bird's eye view of the entire assembly, either removed from the window or at least with the window open, would be best. From there I'll do my best to make a determination for you. 

Keep in mind with some older versions of these operators, the covers were never meant to be replaced, and so if they pop off there may be no option that will attach properly. This unfortunately may leave you no other recourse than to replace the whole assembly. I'm hoping it won't come to that, but better photos will determine things one way or the other.