For notebooks it can be really complicated to undervolt, because they lock down the BIOS a lot on there. Because in a notebook, you don't just get the board separately and can tune the BIOS to your liking and to your other hardware, you get a distinct combination of all the components and the cooling, and everything is fine-tuned already. Doesn't mean that this fine-tuning is perfect, but it is set up very specifically, and they don't want the end user to mess with that, because that can easily mess up the whole system concept, and you'd basically lose your warranty. Because if you try to set up your CPU to perform better by loosening power limits for example, you could then overload the PSU of the notebook, or the temperatures for some things might become too much (usually the cooling in there is all connected).
So they really don't offer a lot in the BIOS that could break things in this manner. To undervolt, I've seen people make modded BIOS versions that expose all the settings, but I would really not advise this if you don't know what you're doing. Like I said, on a desktop PC it's relatively easy, on a notebook, not really. In a notebook's BIOS, you tend to only have a fraction of settings available compared to a desktop motherboard's BIOS.
