De-solder, slide a shrink-wrap tube over the main wire, re-solder everything back together and shrink-wrap the connection point. The shrink-wrap adds a lot of strength to the connection, insulates it from accidentailly touching a ground point and makes it look a LOT cleaner. Does a half decent job keeping out dirt and preventing corrosion, too.
That's what I've always done. I MUCH prefer soldered connections with shrink-wrap to crimp-on or twist-on connections. If done right, you won't be revisitng those connections again for a couple of decades.