It all depends how it was UV mapped.
I am sure you can select that face in Milkshapes UV editor and Mirror the UV.
It will just boil down to practice and understanding, then you will be doing it in your sleep.
Keep at it. It will come together.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.