Motherboard pci slot 0 gpu which one slot 0gpu?

Hi poison2015, are you asking how to find out which physical GPU is GPU0 in your rig?

Stop the Miner from the web GUI (Miner Actions, Stop Miner)
Start a SSH shell to your rig and login as user, type gpu-fans-find [GPU number]

Example: gpu-fans-find 4
(This will stop all fans on all GPUs and only spin-up the fans on GPU4 for about 10 seconds)

Probably quickest and easiest to just reboot your rig when you have finished labelling your physical GPUs.