Instant ocean salt?
Theres really no special methods to converting a tank to salt. Just clean it and changing out the substrate would he a good plan.
I have found that some freshwater bb works in salt water. Specifically the bacteria that convert ammonia into nitrite. The bacteria that convert nitrite into nitrate don't work though.
People argue about salt, but imho
instant ocean is great. Its by far the most commonly used salt in the industry and problems with it are few and far between.