This may be Pre malignant lesions like leukoplakia...

You should ideally contact and oral pathologist for this problem. There is no specific medication to heal such lesions and only "wait and watch" is the recommended approach, keeping in mind very specifically that the Habit should not be continued again and a good diet should be maintained. The time since you have left tobacco is highly insignificant in comparison to the duration that you have been consuming it, so you need to be patient to be able to see any positive results because that will not happen overnight. Kenacort is not the medication for this problem and more importantly it should also be avoided because it has its own series of side effects. Regards

Kindly take opinion of an oral pathologist .. till then, u can use ointment candid for application over the black patches.