Translation
For eons you turn the prayer beads, but the machinations of your mind don't stop.
Toss the prayer beads from your hands, instead turn the prayer bead of your mind.
Explanation
Here, the polemical Kabir Saheb takes aim at empty ritualism - a frequent target, while also conveying a deeper metaphysical truth. He says that the supposed meditative practice of turning prayer beads is a total waste of time, so long as your mind (read ego) remains untransformed. Instead, he exhorts us to turn (focus) the mind inward towards self-inquiry. That is true meditation.
At a deeper layer, the turning of the prayer beads points to how we run around in circles in the external world looking for happiness, while never examining our internal world. Our mind is constantly "revolving" -- scheming, machinating. When we give up these fruitless revolutions in the external world and begin to focus inward, true spirituality begins. This is also the essence of vairagya or detachment.
man kā manakā symbolizes the aham or "I"-ness that points to the individual ego (self). Kabir Saheb tells us to turn it so that it points to the Self (Atman)