If the arm is still on a Layer of its own you can create the necessary Adjustment Layer and Clipping Mask them to that Layer.
It is difficult to provide precise information without seeing the image but perhaps this approach may be of help. I assume that the arm you placed in the image is on its own layer. Based on that you might:
1. Use the eyedropper to sample a suitable skin tone in the image.
2. Then, choose the arm layer and click on the Lock Transparent Pixels symbol in the Layers panel.
3. Next, Edit > Fill > Foreground color with its blending mode set to Color.
4. You may use Levels or Curves to alter the tone level of the color.
If changing the lightness or darkness of the arm using Levels or Curves alters the color, as well, switch to Lab Color Mode and use Levels or Curves on the Lightness (L) channel. The beauty of Lab Color is that it allows you to alter the tone level without altering the color. Then switch back to RGB.
A warning, though: Switching to Lab and back to RGB does, especially when working in 8 bit, affect the image.
thx, this is my first time using photo shop though, so it's a little hard to understand but ill try my best, THANK YOU ALL