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It looks like a downward-pointing finger in the tool menu in the upper-left corner of the dialog box. Use the "Brush Size" and "Brush Pressure" settings in the right pane of the window to adjust the size and sensitivity of the brush. A smaller brush will yield better results with this tool. For example, gently drag the parts of the calf you want to eliminate toward the mask lines you drew.  It may take a couple times before you get the feel of the Forward Warp tool. Because the tool alters the shape of the pixels over which you drag it, the image can become overly-distorted very easily. Click Restore All in the right pane to undo the changes you've made and start over.
Click the Forward Warp Tool. Use the Forward Warp Tool to drag unwanted parts of the image toward the mask lines.