I dont understand EV training as I know how to get the supplements for the EVs but my Pokemon already have EVs distributed between everything from leveling up so I dont know how to just train 2 stats. I heard that you can use the berries to lower the EVs of a stat and I used a lot of them but when I check the EVs nothing changed on that certain Pokemon I used it on.
this might be a tad bit too simplistic of an answer but here
this page contains all of the basic info on effort values and should be up to date (unless sword and shield messed with ev training) the best thing for you to do is to watch a guide on youtube on how it works and mirror the steps taken into your own game. I doubt that there are guides that have been done in sword and shield but to my knowlege the last time that ev training was changed was back in gen 3 (Ruby Sapphire Emerald) so any game's toutorial from then on should be fine. I hope this helps you find the info you need.