Right corner doesn't go in alle the way?

As glass is obviously present your best bet is to use one of the guides to remove and reinsert the screen, which I believe is the first part to remove. If you’re not concerned how it looks then just ignore it the 6 or even 6s doesn’t have any water resistance anyway. If I were to guess the cause then it’s likely due to the bendgate issue those particularly with the plus varient suffered from at launch.