How do I get dust out from under a fitted screen protector?

A bubble with a dark speck at its centre is a dust particle holding the protector off the screen. It won't settle out, it won't work its way to the edge, and pressing it only spreads the bubble around it. It has to come out mechanically.

Telling dust from air

Look at the bubble against a bright background. Air pockets are clear, usually near an edge, and often shift slightly if you tilt the phone. They will be gone within a day as the adhesive continues to wet the surface.

Dust bubbles have a visible dark point at the centre and don't move. Those are the ones to act on, and acting sooner is better: adhesive that has been holding a particle for weeks doesn't recover as well.

The tape method

Take a strip of ordinary sticky tape, parcel tape, Sellotape, anything with reasonable tack — and fold one end over on itself to make a tab you can hold.

Press the rest of the strip firmly onto the nearest corner of the protector and pull upwards slowly. The corner peels away cleanly. Lift only as far as you need to expose the particle; the less of the protector you separate, the less dust can get in behind it.

With a second, fresh piece of tape, dab the particle off the display. Don't wipe, which drags it across the glass, and don't blow, which adds moisture and simply relocates it.

Laying it back down

Lower the protector from the lifted corner and let it fall not pressing it. The adhesive rolls back into contact and pushes air ahead of it, exactly as during the original fitting.

If a new bubble appears where the old one was, you've introduced a second particle during the lift. Repeat once. If it happens again, the working environment is the problem, move somewhere less dusty before trying a third time.

How many attempts a protector survives

Tempered glass adhesive tolerates two or three lifts. Beyond that it starts holding dust of its own, loses tack at the edges, and becomes prone to lifting later.

If a protector has been fitted for several months, the adhesive has usually set enough that lifting leaves a permanent haze in the affected area. At that point a fresh protector is a better use of ten minutes than a rescue attempt.

Preventing it next time

The particle got there during fitting, which means the preparation was the weak point instead of the technique. Fit in a bathroom a few minutes after a shower, and inspect the screen at a glancing angle against a light before the protector comes out of its sleeve, dust that's invisible looking straight down is obvious from the side.