Jiwan Kumar, extraneous lines on smartphone screens are usually an indication that the screen has failed and needs to be replaced. Of course, before you do that it will be worth your time to try and reset the phone, and if that doesn't help you should back it up then restore it to factory settings and see if that helps.
If you add a photo of the problem you're seeing on the screen that may help us with diagnosing the issue, but based on just what you've said it sounds like you should replace the screen.
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