Cosplay Chest Armor Shape Edits for 3d print model

I already have a printable 3D file for a wearable chest-armor cosplay, but the back plate needs to be replaced by another one. I have both files. The armor piece will be 3d printed to be wearable, so... (Budget: $10 - $30 USD, Jobs: 3D Animation, 3D CAD, 3D Design, 3D Modelling, 3D Printing, 3D Rendering, 3ds Max, Blender)