If the dust is on the focusing screen, the safest first step is to use a strong hand blower (for example, a rocket blower) with the camera held lens-mount down so loosened dust can fall out. In most cases, that’s as far as you should go.

Focusing screens are usually plastic and very delicate, so brushing, wiping with paper, or scrubbing can damage them easily. Dust on the focusing screen will not show up in your photos, only in the viewfinder, so it’s often best to leave minor specks alone.

If your camera’s focusing screen is removable, you may be able to remove it and clean it very carefully, but this is risky unless you follow the camera’s instructions closely. If blower cleaning doesn’t help, the safest option is to have a repair shop clean it. Replacement screens are generally possible if one gets damaged, but avoiding damage is better than trying aggressive cleaning.