I would suggest that the first thing you need is suitable industrial experience such as electrical or hydraulics.
If you do not come from a suitably technical background, no training course in the world is going to help. There are many, many more technically competent people out there all looking for jobs too.
There is no such thing as an ROV industry recognised course, there are training schools that train using IMCA ROV training guidelines, but IMCA neither recognise any schools nor any specific training qualification following their attendance. Any school that tries to say you will be IMCA certified after attending their course is lying.
Equally, there is no such thing as a standard pay rate for any position among the ROV companies.