I setup a Team today, but 4 students joined my class late. Therefore, they couldn't see the new assignment. I can't see to find a way of assigning them the assignment apart from setting a new one (which the whole class would see?)
There is no way to assign to a subset of the users in a class team, but this functionality is coming. Students added after an assignment is assigned will also not receive it, so there is no way to accomplish what you need.
If the other students haven't turned in their assignments you can delete it and issue a new assignment to the whole class.