black or dark tongue spot could be due to a tongue injury that causes a blood blister to appear. Hyperpigmentation of the tongue is a side effect of some medications and can cause dark patches on your tongue. Sometimes, smoking or other conditions can cause staining in your mouth and cause your tongue, cheek, or other parts of the oral cavity to have a dark discoloration.Most of the time, black spots and patches on your tongue are a temporary condition. Good oral hygiene, changing your medication, or stopping smoking is enough to get rid of the black spots on your tongue, inside cheeks, or lips. However, if you have a black or discolored lesion on your tongue that doesn’t go away, you should have it checked

Nothing to bother.no need of any treatment