Thanks for the info on the LED. This is good to know.

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Retouching solder is easy if you have the right tools.

This is all you have to do:

Use a high-heat iron to melt the solder you want to fix. Use a solder vacuum tool or some other tool to remove the solder. Reapply new solder.

You do have to remove the old solder because the crack may easily reform if you just melt it and then leave it there. Carbon may have built up in the crack and simply heating it up won't remove that.