Determine voltage with which to run COB LEDs
COB LEDs are usually current-driven, not voltage.
You can sacrifice one and increase current slowly until failure and step down 30% from that.
You can also count how many LED chips are there, as they are usually visible underneath the phosphor, then check the voltage. That will tell you roughly how many strings in series and parallel, usually they take about 100-150mA per string.
Note that cooling is an important factor in how hard you can drive a COB LED.