Hello, I bought the Moment wide lens and noticed that photos taken with the lens on my iPhone 6s plus have dark corners. What is the best way to remove the vignette?
It depends on how severe the vignetting.
If the edges are a bit dark but still show detail then Apple Fanboy's suggestion would work. Lr can do a very good job rather easily.
If the edges are very dark then the image quality (luminance noise, chroma noise, saturation, ...) will be significantly reduced. These can't be easily dealt with and it's often impossible to completely "heal" the area. Lr can handle this rather well, as well as almost any tool, but it does require additional work in Lr to accomplish.
If the edges are black, nothing can "remove" the vignetting; you either have to live with it or crop the image, which reduces the wide angle effect.