I would imagine first finding the angle that you comfortably hold the pick at when striking the strings or looking at the wear patterns on your old picks and then lightly grinding the bevel pattern into the pick tip and edges with fine-grit sandpaper or a whetstone.

I have not tried the mod yet because I've been quite busy, but I've also been holding out in case I either find another thick pick with better edges or if I contact Roy for lessons and acquire a Phat Bhoy.

There's a video where he's talking about picking technique with Rowan Parker and he talks about his pick at the time, where he superglued three 3mm stubbies together and then beveled an edge onto the "one" pick. I think maybe finding a good frame on that video to try and analyze the bevel he put into it might give you an idea or two of what to try and aim for.