Lift up on the carpet edges in the tear with a utility knife. Make sure the carpet surrounding the tear is loose.
Cut a piece of carpet-seaming tape the length of the tear. Slide it beneath the tear, half the tape on both sides of the torn carpet.
Plug in the seaming iron. Once it heats, carefully place it inside the carpet tear. Move the iron over the seaming tape to heat and activate the glue. Remove the iron carefully from the torn carpet.
Press down on both sides of the carpet tear to ensure good carpet-to-tape connectivity. Place a heavy object onto the repaired carpet if necessary.
Remove the heavy object and inspect the carpet to make sure the repair will be permanent. Fluff the carpet with your fingers to hide the repair.