The shang gou weapon entry reads:
Forged in pairs, these solid metal blades end in curved hooks, while the hand guards are hammered into outward-facing spiked crescents.
Benefit: Both the crescent and the tip of the hilt are sharpened for combat. They can be wielded as single weapons or with two-weapon fighting styles. The weapons gain the disarm special weapon feature when used individually. A pair of shang gou can also be formed into a single one-handed weapon to gain the trip special feature.
What is the action (if any?) to combine a pair of shang gou into one one-handed weapon as mentioned in this entry? I couldn't find any answers on the Paizo forums or on this site.