Unfortunately these lights are sealed units, so to "repair" would mean cutting/seperating the unit apart and then doing a repair. If you have experience with circuitry you can remove the circuit board , de-solder the faulty bulbs and install a new one provided you can source a like for like match led bulb.
The other option is to replace the entire circuit board for just that section of the light but that would mean acquiring a working circuit board probably off a broken or damaged unit, I was able to do this on an e92 lci taillight many , many years back but i don't have any pictures of the process to share.
The last and final option but also the easiest is to disable the cold and warm bulb check(s) using NCIS Expert, this will remove the warning light on your cluster and the light will still function with some of the non functioning leds but looks horrible.
