I can't tell you how to translate "fix you" into chinese but i could tell you a little bit about the song : its basically a song about hope, it could have a million explanations, but at the end -for me- its about being there for someone that has experienced a lot of pain, so i see the FIX YOU part as a way to declare something like " I will help you, emotionally, through this time until you, eventually, realize that we always move on and things do inevitably get better as we hold on..." aaaaaaaaaaaahhh... this is when the ♪ "lights will guiiiiiiiide you home, and igniiiiiiiite your bones" ♫ makes perfect sense !!!! like 'don't force it, that light showing you the way is gonna be the same light shining inside you when you finish understanding... ' (ignite your bones)
... just my lovely appreciation! ;-)