I’m just getting started with LingQ. Yesterday I was working from my PC instead of the IPAD. The PC was unresponsive and I submitted these as known words in error.
Welcome to LingQ! I hope you’re enjoying it 
There isn’t a way to reset a single lesson, but you can simply highlight the words again to turn them blue, then you can save them as LingQs. There is the option to reset a language on the Account page, but we don’t recommend this unless you’re absolutely sure you want to remove all the data from that language slot.
If you have any other questions, be sure to let us know!
Great!, since this was my first attempt at Latin, I can reset the language