@abhishekga27682 that is a broken AMOLED screen. As you will experience, the "Dot" will get larger until the screen stops working. Time to replace it. Since iFixit does not yet have a specific guide for that, use something like [https://www.youtube.com/watch?v=LtU84mMwD4w|this video] for the repair. Replacement displays are readily available at many online stores.
While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.
Repair is War on Entropy!