Al-Bukhaari may Allah have mercy upon him reported 'A'ishah may Allah be pleased with her as having said that the Prophet (peace be upon him) had said: "There is healing in the black seed for every disease except death.” (Al-Bukhaari and Muslim)
In another narration it was said, 'What is the black seed?' He said, 'Shoneez' (a name for black seed; scientific name Nigella sativa). Someone then asked, 'How can I use it?' to which he answered: You take twenty one grains (black seeds) and put them in a piece of cloth then in water for one night. When you get up in the following morning, you drop one drop in your right nostril and two in your left nostril".
Al-Haafith Ibn Hajar (may Allah have mercy upon him) said, "What is to be understood from this Hadith about the black seed being a healing for every disease is that it is not necessarily applied alone as a treatment procedure for every case. Rather it may be used alone, in combination with something else, pulverized, directly without pulverizing it, mixed with food and drink, or as dressing, etc."
Allah Knows best.