Raspberry Pi Heatsink Kit Aluminum and Copper Heatsinks for Raspberry Pi B B+ 2 3 with adhesive thermal tape. 4-Pieces Each
Clean the surface of the intgegrated circuit with alcohol then let it dry. Once dried peel and stick the heatsink carefully. Adhesive bond will form after 24-hours and heatsink will be very difficult to remove.
This kit fits almost all RPi but you may end with unused heat sinks on some models.