Thanks for asking the query,
Black spots on tongue can be due to pigmentation, it can also be seen in a condition known as hairy tongue is a illness which comes from smoking
, vitamin deficiencies , taking certain medications like antibiotics, tongue can also turn black in conditions like oral cancer
it is often combined with lump formation and difficulty in swallowing.
I would suggest you to visit to Oral and Maxillofacial Surgeon and get checkup done .
Maintain a good oral hygiene and clean your tongue with a soft bristle toothbrush or a tongue cleaner.
Quit habit of smoking, irritating or cutting tongue if present.
Hope this helps out .