Is there any way or addon to facilitate the attachment/alignment of armor to a model? I am trying to fit this armor into the model's arm, but I just can't get it too tightly firm around the arm, I know it fits, the armor piece and the model came in the same size, however, I just can't make it work.

I have tried scaling up the armor piece, but it just won't fit correctly, can anyone tell me if there is a better way to do this?

here is a reference image of how its supposed to look:



here is my attempt: 







armor file:



problems related to the first answer
Juding by your model, rough scaling should work but since the scale has already been altered, the best methods you have are :-


  
  Using Shrinkwrap:- Delete the outer faces and use the shrinkwrap modifier to stick to the faces to the main model's mesh directly or use a lattice. Then add a solidify modifier to give it some thickness
  Retopologizing:-
  
  
  
  Turn on snapping and change the mode to face and then snap the individual faces/verts on the main mesh and use solidify to give it some thickness.