The starting point is ensuring you have a suitable background of qualifications and experience from a technical background. Without one of them, no course in the world will get you a job. Even with it, the courses do not make as much of an advantage as some of the training schools like to make out.
There are many, many people trying to get a start in ROVs. Yes, there is a shortage of personnel, but the industry can only take on a small number at a time to train up and get experienced, companies may take on 10 trainees, but there can be several hundred people apply for them. There are also a large number of ex forces people who have the suitable technical background and are all after these jobs.