How do I fix a green line on the side of my iPhone 13 Pro screen?

Start here.

iPhone Repair and Service - Apple Support

Just to confirm that this is a hardware issue, take a screenshot on your iPhone by pressing the Volume Up and Side Button. Then view the screenshot but in the other screen-orientation view so the lines don’t overlap. If the lines are present in the screenshot, that would indicate a software issue, which can easily be fixed with a Forced Restart. If the lines are not present, that would indicate a hardware issue. That would need to be taken a look at your nearest Apple Store’s Genius Bar or Apple Authorized Service Provider.

Apple Support Resources:

Force restart iPhone - Apple Support

Genius Bar Reservation and Apple Support Options - Apple

"The problem that Green line had has been fixed automatically and all thanks to you guys!"

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So, it just went away in an instant? If so, then it may have been a hardware error. What app(s) was opened while this occurred?

Go to Apple repair shop, or to store, where you bought your IPhone.

Tanveer-9044 wrote:

The problem that Greenland had has been fixed automatically and all thanks to you guys!

That’s great news. You’re very welcome.