How do I fix this
top right side of my iphone 6 plus is darker than everything else u can see through it but its really dark
The most affordable and reliable Option would be to utilize Apple's Out of Warranty Repair Service!
It would cost a flat $150. I can't even buy the screen for that much, not including the 100 labor i'd charge to fix it.
Here's a list of Apple's Out of Warranty Costs:
In summary: To the Apple Store, and Beyond!