Hello and welcome to Apple Support Communities, asnaansari05.
If I understand your post correctly, there is a dark circle in the center of your iPhone screen. I’d like to help.
I'd recommend restoring your iPhone. Before you attempt any restore, I recommend you save and back up the most recent data on your iPhone. Steps on how to back up an iPhone can be found here: How to back up your iPhone, iPad, and iPod touch
Once the backup has been completed, you can restore your iPhone. Steps on how to restore an iPhone can be found here: Restore your iPhone, iPad, or iPod to factory settings
Once that's done, I'd recommend setting your iPhone up as new, and testing it out before restoring from a backup. Check out this article for those steps: Restore your iPhone, iPad, or iPod touch from a backup
Let us know if that resolves this issue for you.
Thanks for using the Apple Support Communities. Take care.