If you have a college degree in mechanical engineering already, you are qualified and should seek to work in the field. One never knows all there is to know and not all they even need for a particular job. There is lots of on-the-job learning. Keep working, keep studying. Learning is lifelong. If you do not have a degree in ME you may still be able to work in ME but you will have more catching up to do . You might want to pursue a MS in ME if your degree is in a related engineering field. If you do not have an engineering degree, you will have to start further back by taking undergraduate courses.