All submerged equipment and associated piping, instruments, access areas, etc have to be cleaned and checked for meeting functional requirement. Similarly power supply systems have to be checked for its integrity to avoid short circuit or arc flash hazards.
Only after checking everything, more than as we do for a new plant, and satisfying ourselves, energization and connecting loads to be done gradually. It is always better to go slow instead of hurrying so that there will not be setbacks later. Whatever we do at home in such scenario, same concepts can be followed.