hi there, a ruptured sebaceous cyst
needs to be completely evacuated and the skin apposed together and sutured otherwise it will get infected leading to scarring and may be an abscess
. If is the skin deficit is too large then you may even need a skin graft to cover that area. Do take a surgeon's consult and get treated accordingly. Now for the time being you can get it cleaned with antiseptic lotion and get a light dressing on it . Try not to sit on it or put pressure over it. Take care.