Dark shadow on the right

i’ve had this laptop for quite a couple years however a while back I noticed there was a dark shadow in the right corner of the screen. It first appeared when my sister was carrying the laptop around school. It didn’t bother me much as I could still see everything just fine however I now intend to fix/ find out what is causing the issue. Could anyone give any advice on how to fix it on a link to a YouTube video showing how to fix it?