You practice. Best to practice bringing the mind to that which will make the mind pure. The Supreme pure is the best for making the mind pure. So in the condition that you described, what should the person do? They should continue to chant, calling from their heart: “My dear Lord Krishna, I know that my mind is all over the place and that it is not with You. That’s my condition. I am disclosing my condition which You already know because You are in my heart. But that's my condition. Please help me. Please pick me up from this dark place of an uncontrolled mind, by Your supreme compassion and purity.” That's what one should do.
Adapted from a lecture entitled “Limbs of Surrender: Humility”, given by His Holiness Romapada Swami in Chicago during March 2012.