Bubbles can either come from air enclosures or dust particles. Please try pushing out the bubble, as shown in the video (min 4:00) or step 9 in the text instructions.
If you can't push them out, it's very likely a dust particle. As long as it's near the edge, you can try the method shown in this video.
Air bubbles can usually be removed well;
Big bubbles:
If you have already removed the protective cover foil, wrap a credit card into the dry wipe(!) to push out the bubbles. Then try to “catch” smaller bubbles with bigger ones, and then push from the center to the edges.
Small bubbles:
Wrap the dry cloth around your index finger and gently rub the bubble until it disappears.