I think the best way to learn will be index on 1, middle on 2, ring on 3 like Ben does in the video. There are alternate ways that could get it done (for example, using your index on 1, then moving it up to 2 and ending with the middle on 3), but the normal consecutive finger movement is really important to get down, because you’ll eventually need to use it in all sorts of places.
It’ll feel more natural the more you do it, and be sure to keep economy of motion in mind—the more motion you save by keeping your fingers close to the frets, the better your technique will be.