ELIMINATING AIR BUBBLES
If you see that you have an air bubble, as seen in the photo, you have to eliminate it immediately. Put some glue onto the brush and brush the surface a couple of times so that it sticks, hold it there a moment, allowing it to stick. The bubble will disappear.
Allow it to dry and it will disappear. However, if the bubble was in the centre, we would try and get rid of it by continuous brushing the area with the brush. Doing it this way we are adding pressure so that it sticks. If the bubble does not go away then burst it with a pin and add some glue.