While the description tells you what to do, there's a certain way to do it. You need to have an enemy on each side of you, dodge one's range attack which will then hit the other enemy on your other side.
So basically; dodge left enemy's range attack > Range attack then hits the enemy to the right, or vice-versa.
I found a nice grinding spot on Sequence 6, right after you pass through the gate, get spotted by the enemies to your right. The gate will close and 3 enemies will spawn to your left, one being a bowman. Just keep blocking the enemies attack by rapidly pressing
+
or
and you'll also dodge their ranged attacks. Then simply die or restart the checkpoint and repeat.