I had this issue before. I found out it was malware that's causing it and reformated my whole PC. It was a test PC so I didn't have any important files on it.
I suggest you take a look at your thermal paste. My friend had the same issue with his CPU temps going up to about 90 - 95° C. When I suggested him to take off his cooler to check, he discovered very little paste and has dried off. Undervolting should be the second last resort.
Is this a year-old laptop? If so, I don't think you will need to replace the thermal paste. Something else must be off. But I wouldn't suggest trying to thermal paste your GPU unless you've done this before.