Resolder the entire relay. Use a small iron (around 20-25 Watts) on the smaller connections and a solder gun (150-300 Watts) on the larger connections, but move fast (lotsa heat!).

Use electronics solder when you resolder (not plumbing solder). The rosin in the electronics solder helps the melted solder flow and adhere to the copper trace and wires.

Note that sometimes you'll find a tiny part of the trace burned away (middle pix with the red circle). This happens when the wire from relay to solenoid loses insulasion and shorts against ground. The extra current blows the fuse and sometimes burns the coppoer foil trace. You can repair it, as shown in the third picture.