Hello Mr. Ashish, although the x-ray is not clear, its clear you have a partially erupted wisdom tooth or the third molar and because of the flap of tissue over it, it is difficult to keep it clean, food lodgement inside that flap causes decay in the third molar. Since there is no space for it to erupt fully, the situation will persist like this. Because of the difficulty in access to instrumentation it is usually advised for extraction.
Next Steps
Plan the extraction with your dentist at the earliest.