Here's a couple of vids that helped me figure it out::

Be methodical and it shouldn't take to long. You will want to make changes, then run the game to see if it stable noting big stutters, freezes, and crashes then move on to the next setting changes. I recommend you watch a few vids on Youtube about how to undervolt and take notes especially while setting up your cards sweet spot to track your changes. ONLY download MSI Afterburner from the MSI website to be sure you don't get any unwanted hitchhiking malware. Most of the other utilities are cumbersome and non-intuitive. There are a number of utilities and ways to accomplish undervolting, but I highly recommend MSI Afterburner - it works with everything (games that is and other software) is easy to use and it's free.

There is a period of trial and error while you find the sweet spot for your card, but once it's done it is set and you can pretty much forget about it. The card was running at extremely high temps (90+ C!) in IL-2 even with fans blowing at 100% before and now I can hold temps in the mid 60's C range in IL-2 144 FPS on a 32' inch monitor and low 70's C in MSFS 2020 82 FPS, so it is definitely worth it. I undervolted my EVGA 3080 and the results were awesome.

Msi afterburner rtx 3080