Slowly feed solder wire into the heated wire. The wire strands should readily absorb the molten solder.

If the solder pools on top of the wire strands, the strands aren't hot enough to melt the solder. Try moving the soldering iron so that the tip touches more of the strands.

Feed solder wire along the exposed wire until everything is thinly coated.

Once the molten solder saturates the wire strands, allow the solder joint to cool down and solidify (2-3 minutes).