It is common to have spill on your subject when using blue or green screen. The KEY36 plugin will automatically remove (or mask) green spill, however, if the spill was extreme it can cause transparency on your subject once removed.
Running the Spill Brush Prep action will select the Color Replacement Tool with the appropriate settings and also put you on the Source image. You will then need to set the foreground color to the color you want to paint with, and set the background color to an area containing spill. You can then paint over the spill to change the color of those pixels.
Once you are happy with the result, you can play the Color/Spill Brush Done action to continue editing the green mask.