To isolate (isolate = place by itself) a concern (concern = something that causes concern) is basically to solve one problem at a time. Rather than letting yourself be overwhelmed by many things that may be wrong, you look at one piece of it and try to solve that. There may be additional meanings based on context, but I think that's the basic principle. I hope that helps. Good luck with your studies.

This isn't a common phrase, so its meaning depends on the context.