Driving 36V LED from 12V Supply
Solutions that only supply partial power to the LED (at least 5W) would be acceptable.

It may not be possible with what you have at hand.
Most 36V-COBs start to illuminate at 25-28V. For yours, it could be around 28V/10mA (I'm just guessing as there's no datasheet available.). So there's no chance to drive that LED with your LED driver as the max allowed output voltage is 12V.
Even if the LED driver is part of another system and cannot be replaced, you may have an option to use a separate, appropriate LED driver only for that LED. Or, if it's not vital to use that LED, maybe you should consider using a different one that your LED driver &quot;likes&quot;.
But remember that,

You can't use your existing LED driver,


You can't convert 0.9A constant current (12V max) to 0.3A constant current (36+V max). If someone knows a CC-to-CC converter, please let me know.