You can do this Shabar mantra chanting for 11, 21, 31, or 41 times, the spot and time of mantra chanting should be the exact same for the volume of days you would like to do sadhana. You may use Rudraksha or Tulsi rosary to chant the mantra. It's https://directorypixels.com/listings13077031/most-powerful-sarv-karya-sidh-shabar-mantra-karya-siddhi-shabar-mantra-most-powerful-shabar-mantra-for-dummies