i have an injured chick!!!! help

[atlanta chick]

i have three chicks (delaware, barrock and a buff orpington) 2 weeks now. the delaware was quickly the boss and now the other two have been pecking at him just above his wing and neck....

i separated them and cleaned up the injured one....the injured one is very vocal and upset to be apart.... the other two are fine...
what do i do now.... how will i know when to put them back together???