Dandruff is due to excessive oil production. Small boils over shoulders are pimples again which is due to excessive sebum production. Stop applying oil to your scalp as this increases dandruff. Use sunscreen to prevent bkack soits. Black spots on face can be due to many reasons. It could be due to post acne pigmentation, freckles, melasma, etc. Hence send pic for further treatment.apoky sunscreen every 3 hours. For dandruff you can use ketoconazole shampoo.
Next Steps
Meet dermatologist for further evaluation