Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
If you mean 'where the lens connects', the inner glass surface of your lens assembly, then clean that carefully so as not to scratch the sensitive fine optical glass... with a camel-hair brush, ideally, where dust is concerned.
Where dirt more than dust that can be brushed away is concerned... please describe it, and I will instruct you how to proceed, as appropriate.
As for overexposure... Try changing the white balance setting, or cancelling / erasing all White Balance settings on your very configurable Canon DSLR camera.
(The one sure way of doing this is to Settings Reset the camera... that puts all settings back to factory default. Let me know if you would like to try this, and I will get you instructions that will work on your camera model.)
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