Cut out the swatch of berber carpet that needs to be replaced.
Lay the cut out carpet over any spare carpet you may have left over from installation. If you don't have any leftover, find an inconspicuous area in your home where missing carpet won't be detected, such as under a large bureau or dresser or in a closet.
Cut a new swatch of berber carpet using the old, cut out carpet as your guide. Use a steady hand and make sure they are cut exactly the same size.
Spread a layer of the glue on all four edges of the carpet and press it down into the cut out area that it needs to cover. Make sure the fibers of the swatch are facing the same direction as the rest of the carpet. Hold it in place until the glue just begins to dry, then leave it to dry fully.
Sweep your hand over the spliced area to make sure it is dry and that the fibers look the same as the rest of the carpet.