Advice a friend who respond to conflict by avoidance on why it is not healthy in susbtaining positive relationship

In advising this friend, explain that avoiding conflict is not healthy because then the conflicts are never resolved. While they may seem to go away in the short-term, it's more like pushing issues under a rug. Eventually, the rug won't be able to cover all these issues, and they'll cause an explosion of emotion that may cause the friend to say or do things that they will regret later on. You could also explain that there's a way to be confrontational without being aggressive, but that communication is necessary to maintain a positive relationship with others.