Thawing areas
To thaw areas, do any of the following:
Using the Thaw tool
Select the Thaw tool 
, and drag over the area. Shift-click to thaw in a straight line between the current point and the previous point that you clicked or Shift-clicked.
Thawing all frozen areas
Click the None button in the Mask Options area of the dialog box.
Inverting frozen and thawed areas
Click Invert All in the Mask Options area of the dialog box. If you used a selection, transparency, or alpha channel to define the frozen area, the alpha channel name in the Channel pop-up menu changes to Custom.