Thanks for asking the query,
Causes of tasteless of tongue is due to allergies, nasal polyps, ageing, nerve damage
, vitamin B12
and zinc deficiencies.
Sour items, salty and junky food should be avoided.
Take plenty of raw vegetables, fruits, iron rich diet.
Continue with the course of multivitamin
Take lukewarm saline rinses.
Hope you find this as helpful,