They can find new homes in places like Canada, Greenland, Northern Europe, and Russia. After all, in order to raise sea level, there has to be a lot of land ice that melts. And once that melts, a lot of new land that was uninhabitable now becomes available.
I guess I should have ended with the sarcasm tag. Ain't ever happening, this rising of the seas, at least not in the foreseeable future. AOC is nuts.