These days you can purchase thin cell phone protectors made out of a material that adheres to your phone screen without chemical glues or adhesives. That means these protectors are disposable. But if you want to conserve your screen protectors, you can reuse them on different phone screens with the same dimensions.
Peel the protector off of the phone by the corners.
Clean thoroughly the screen of the phone you intend to put the cover on with a microfiber cloth. Many screen-protector packages come with both microfiber cloths and small squeegees, so you may have these items already.
Fit the screen protector over the new screen, making sure the sides and corners of the protector are flush with the sides and corners of the screen. The screen to which you are applying the protector must be the same dimensions as the screen protector.
Use a small squeegee to wipe the top of the protector and remove any creases or air bubbles.