My father had a problem of esophageal candidiasis last year. Then he recovered. Now today he is again feeling symptoms of candidiasis. What to do now?

Comprehensive ... Better to see PCP and have a comprehensive History, Physical, labs and appropriate Imaging studies to have exact diagnosis of what seems to be a recurrence of Symptoms. Then see the specific Specialists like Gastroenterologist or Infectious Disease Consult as the case may be. .
Needs work up . It is already well accepted that Candida are known to colonize the esophagus of 20% of healthy adults. Once colonization has been established, impaired cellular immunity permits invasion of the epithelial layer, such as HIV infection. Proton pump inhibitor, H2 antagonist, vagotomy , Antibiotics and corticosteroids increases the risk of Esophageal Candidaisis. .