Please note that screen protectors are always precisely adapted to the display dimensions of your Gigaset phone. The protective film can usually be recognized by one or more colored stripes. If you are not convinced of the quality of your display, please first check whether the screen protector is still attached to the device. If necessary, remove the protective film from the display with your fingernail.
With some models you will also find a transport protection foil. Please make sure that this is also removed.
The display protection film sticks to the display due to cohesive forces to leave no glue residues. Cleaning with chemical cleaning products is not necessary.
Here are some sample images for better recognition of the color stripes.