How to join two wires with solder

Put one of the paired wires on one of the helping hand's clamp. Put the other pair of wires on the remaining clamp.

Using both stripped wire ends, wrap and tie both of the ends together.

Solder the tied ends of the filament.

Pull on the two wires firmly to ensure the solder does not separate.

Cut enough heat shrink to cover the soldered connection.

Slip the heat shrink onto the connection.

Using a heat generator, such as a heat gun or a hairdryer, heat the heat shrink around all of the angles until it securely covers the soldered connection.