In order to reach that Brahmarandhra, one has to diligently ascend, Chakra by Chakra to the Bhrumadhya (center of the eyebrows).

To move prana in each of the chakras from Muladhara to Ajna as instructed by Gurudeva is the karmakanda of sadhana

Taking it via the upward moving, sattva-endowed sushumna and going up to the “r[a]” = Eye; “dhi” = after stilling the mind there, “a” [=] again coming [down] to the Muladhar... Bringing it to the Eye + “a” = again taking it to the Muladhar.

Do “shikligar” (the term for sword cleaning) to your self. To do “shikligar” upon a sword, go from the base of the weapon to the tip [in one stroke] and again come back to the base. Now do the “shikligar” of Kriya via the Self and clean the self.

Kabir is saying that Guru is like the washerman and the disciple is like the cloth – meaning: in the way that a washerman cleans clothes, so does Guru clean the cloth-like disciple with soap – meaning: cleaning the self again and again on the stone of meditation, Boundless Light comes forth. -14

[Lahiri Mahasaya's Commentary:]  Kabir, the Atman-Guru in the body is washing [you] like this: once up and once down.