It does have specific conditions. Your DPF lamp has to be on indicating that you need a regen and driving conditions aren’t allowing passive and active regens to keep up. The shorting plug (dumb name for it but oh well) is below the dash on the left side right by your J1939 port.
Below are instructions and a picture of mine:
View attachment 24911
View attachment 24912
You can only do a regen this way if the system is calling for one. You need an external device (such as a code reader with regen capability) to do a forced regen, but theoretically, you don’t need one and the shorting plug will get you through. I’ve never used it because I’ve always had a means to do periodic forced regens to prevent the need while on the road but I’ve seen accounts of folks using it successfully.