Before you add hot melt glue and shrink the tubing, test the connection and make sure it works. Now is the time to fix any problems. The most common problem is reversed polarity. That will mean that one segment will light and the other won't. Switch the power wires and the reverse happens (the other lights and the first won't for example). If you have to desolder a joint, just pull a little on the two ropes and touch the soldering iron to the joint -- it will just come apart. You may need to tin it again.