I bet you faced the same problem: It is nearly impossible to place a display protection foil without any fluff on it.
If you already have fluff on the foil you have to remove it first. Trying to scratch it away does not work. Contrary, you get scratches on your foil which cannot be removed anymore and stay visible even after placing the protection foil on your device.
Best remove the fluff under floating warm water with the use of a bit of dish liquid. Rub the foil with your finger tips (do not use anything with sharp edges). Then wash the dish liquid away. Important: Do not dry the foil after cleaning it, otherwise you'll have again fluff on it (from the towel).
Switch off or even better remove any batteries from your device you want to attach the protection on. Place the still moist foil (keep some water drops on it) quickly and as good positioned as possible on your device. Make sure you place the correct "sticky" side of the foil on your device. If there was enough water on the foil you can still move the foil a biot for short time to correct the placement.
Afterward fixate the foil with one finger so it cannot move anymore and use an applicator (a credit card is also a good choice) to press remaining air bubbles from the center to the edges of the foil. It is likely that some water drops will be pressed out on the edge which may be swabed carefully. Then simply wait. The water dries away and the foil fits perfectly. And you'll see no ( or only at the edges where you normally do not care about it) fluff anymore.
But don't go crazy if this method did not work the first time. It took my also several tries until I removed all fluff from the foil.