how do we know that Chris tried to return to civilization

Krakauer’s personal story makes it clear that McCandless was almost surely not suicidal. Although he admits, in his last postcard to Westerberg, that he is aware that he might never make it out of the wilderness alive, he believes in his ability to survive, and he is too young to truly be able to imagine death, especially because he has managed to survive all of his other dangerous adventures.