Satart lesson over

Can I start lesson over as if I never looked at it?

No, you can’t reset it. You can only reset the complete language.
But you can just go through the same lesson again, then click on all white words to make them blue again and create LingQs for them. So, if you are reading, and come across a word you incorrectly marked as known or ignored, just click on it to make it blue.