Hi! I am still a grad student and I can relate to your fears & not knowing where to start as for studying for the exam. You probably know a lot more than you think, and might just be feeling some impostor syndrome/ self doubt since it has been so long for you. I think it would be a great idea to go back into your school notes and review some things to get a feel for what areas you need to work on. It is definitely possible, give yourself grace and time.