Remove the broken link if it is still partially attached to an end of the chain. With the pliers, hold the link on either side of the break, twist off.
Unscrew the nut counter clockwise from the body of the quick link, opening a space between the nut and the threaded receiver. Use the crescent wrench to start if the nut cannot be turned with fingers.
Insert the quick link threaded end through the end of the chain attached to the tow vehicle.
Insert the quick link threaded end through the end of the chain attached to the trailer, joining it and the vehicle chain together.
Drop the nut back onto the threaded receiver, twist clockwise with fingers to tighten.
Tighten completely with crescent wrench.