Remove the PC board from the device.

Set the board up in a clamp, vice or alligator clips to keep it stationary while you work.

Note the orientation of the existing triac before you remove it.

De-solder and remove the triac and wick out any solder in the contact points.

Clean the flux and solder bits from the PC board taking care not to damage any of the components, traces or mounting points. A soft bristled toothbrush and rubbing alcohol work well.