Someone posted this link from comments before: https://incubator.duolingo.com/courses/sw/en/status
A month ago, it said that they finished recording audio and that it should be updated soon.
So a person from the USA is "mmarekani" (m + Marekani), and I guess a person from the American continent would be "mamerika". But I don't speak Swahili yet, do I don't know for sure.
Edit: It seems that the actual word is "mwamerika". Like in "mwafrika" (African person) and "mwingereza" (English person) you get an extra w when adding m- in front of a vowel.