Blue dot on screen iPhone 6

Hi,

I've just replaced a iPhone 6 screen for a friend, Everything went fine, however we've noticed a small blue dot around 5-6mm above the home button. It can only be noticed with a white background, Now i've done some research and found the following.

- I've pulled the phone apart and used a heat gun on very low heat to absurb any humidity.

- I only use very little pressure to put screens in and not around this area where the dot is.

- The dot goes away if the screen is apart from the housing.

This is the second screen that we've put in it due to the fact the last one had a larger blue dot. This screen is from another supplier and we can say this dot has shrunk in size compared to the first one.

I've done plenty of iPhone screens in particular iPhone 6 & 6 Plus and haven't come across this issue yet!