To add to the answers you've already received, Many LEDs are quite tolerant to voltage overdrive as long as their overall power dissipation remains within ratings. I have some 1-3W white and RGB LEDs rated for ~3V that I can drive by pulse width modulation of 12V at about 200hz without burning them out. Doing this has a significant negative effect on their efficiency and longevity due to I\$^2\$R losses, so if PWM of an overdrive voltage is used for simplicity, it is best to keep the overdrive voltage close to the rated voltage.
For best efficiency at a given brightness, LEDs should be driven at a constant voltage, with the caveat being that they have a non-linear brightness when driven this way and cannot be driven below their minimum turn on voltage. There are generally two approaches taken as a result:
If accurate 0-100% dimming is required, like for RGB LEDs incorporated into a display, the LEDs are typically PWM driven with a 0-100% duty cycle and pulses of a constant voltage chosen so that at 100% duty cycle the LED will have the desired brightness.
If accuracy is less important, the LED can be driven with constant voltage above its minimum turn on voltage and switch to PWM where dimming below that point is required. This is more efficient than PWM dimming across the entire range, but providing accurate 0-100% output control with this method requires calibration and a more complicated/intelligent control circuit.
Note that because of thermal runaway, it is best to use current rather than voltage regulation for power LEDs. Your goal is simply to "reduce heating" of your (COB?) LED, so another way to state it would be that you wish to "increase efficiency", so you should use a constant current supply. Note that the switching converter you choose will have losses and generate heat as well, so find efficiency graphs for it to ensure it will have good/acceptable efficiency at your intended load current particularly, and also over your potential load current range.