I would suggest getting further course/qualifications/experience in basic electrics and hydraulics. These are the two main areas required.
You will mainly NOT be going down to fault finding to individual components these days, most tends to be down to board level, though soldering should be capable for splicing cables, etc.
An ROV Course is basically an introduction so that you have an idea of what ROVs are and what they do. Most employers are more interested in your technical skills and experience.
Read through the Rookie section on here for a lot of commonly asked questions.