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Load your image. Select the Clone Stamp Tool.. If you don’t see this one but one similar to it, right-click it and select the clone stamp tool. Zoom into your image. Try to be as close to the pimples without the brush actually touching it. While holding the Alt button click on that small portion of skin. Than click on top of the pimple. (First image is without holding alt, second is while holding the alt button)
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You might have to press it a few times on top of the pimple, depending on size and redness. Do not drag the brush. Do it one click at a time.

Note: Image credit goes to SkinCareRX.