I can understand being nervous if it's something you've never done before but it's very easy.
Go to your favorite hardware store and get an 18" metal straight edge so you can see the relief in the neck. You can also use the stings by fretting at the first and last frets but it's a little tough if you don't have 4 arms. A capo would help.
Anyway, stewmac has a sting action gauge tool that looks like a metal credit card. They make an imperial and metric one so get the metric. You now have all the tools you need to set up your axe. I like this measuring tool better than a small ruler because it sits over the frets and it's easy to hold in place.
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Or you can do it the good ole fashioned EVH way. Adjust it so all the strings barely buzz, then back it off a bit
Seriously, this is a skill guitarists SHOULD know, and his s320 would be fairly forgiving. If he's able to do a string change on that LotrsII guitar and have it play ok, he is more then capable of doing a simple truss rod adjustment. Just takes some practice!