Burn-in pixels are a common issue with OLED screens. There are several ways to fix screen burn-in on mobile devices. One way is to lower the brightness settings of the device as higher brightness settings can cause screen burn. Another way is to enable pixel-shift which constantly moves the image slightly to vary pixel usage. 

As for the manufacturer's guarantee, it depends on the manufacturer and the warranty policy. For example, Samsung's warranty policy does not cover defects or damage resulting from normal wear & tear, corrosion, rusting or stains. You may want to check your device's warranty policy for more information.
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