Straight out, it is unlikely something like this can be used for a device needing a constant voltage.
The topology, however, is likely a fly-back smps - assuming that it is isolated. That means the led string is floating above a current sampling resistor that controls the output voltage to maintain that constant current (thus constant voltage over the current sampling resistor - likely via a zener + optocoupler).
So all you need to do is to identify that resistor and put in place a divider. That resistor is very easy to identify: it must be between the cathode (led-) and the ground.
After that, you have turned this constant current regulator to a constant voltage regulator.