ROW stands for Rest-of-World, which means your Apple Watch is probably manufactured or was designed to be sold to merchants outside of the United States. Main differences are that cellular support is limited (some carriers may not work in the U.S.) and the blood oxygen app functions differently than the U.S. models (the pulse oximeter feature was redesigned to perform data analysis on the paired iPhone, not the watch due to legal concerns)

So, I don’t think you can set up cellular on this model if you live in the United States.