When done correctly, this repair eradicates the damaged area with minimal or no evidence. Remnants from the installation of the carpet make the job a little easier. If no remnants can be found cut a small portion of carpet from the back of a closet or other out-of-the-way space to provide a repair piece.
Position an empty can (or other container of comparable size) on the nap side of the repair piece and press down firmly, allowing the rim to make a clear impression. Then cut around the outline using a sharp utility knife.
Carefully cut along the outline with a utility knife (image 1). The diameter of a standard can is a good guideline for the size of a replacement piece. The goal is to keep the cut-out area (image 2) as small as possible but still allow carpet tape to be inserted into the space and laid flat beneath the carpet backing
To ensure the carpet tape doesn't work its way back through the opening, cut a length 2 to 3 inches wider than the diameter of the cut-out area. (Carpet tape is available in double-sided and single-sided versions; the single-sided type generally works best for this type of repair.) Peel the backing away from the adhesive side of the tape and carefully insert the piece into the cut-out area, smoothing it flat from below so that it sticks firmly to the carpet backing around the perimeter of the opening. Be patient and work carefully: handling the stickiness of the tape can be a challenge. For a cut-out this size, it generally works best to cover about half the space with one piece of tape (image 1) and use a second piece to cover the other half (image 2).
Once the carpet tape is firmly in place, turn the repair piece so its arrow is pointing in the same direction as the arrow near the cut-out area and press it firmly into the opening. Apply extra pressure all around the edges of the new piece, working the fibers into the surrounding carpet.
After the piece is fitted snugly into the opening trim any fibers that are uneven with the surrounding carpet. To even out the difference, lay a pair of scissors flat across the new section and carefully trim off just enough to "blend" the piece into the adjacent fibers.
Set a heavy piece of furniture, stack of books, etc. over the repaired section for a day or two to ensure it's fully "integrated."