To import into LingQ you must use the mobile website instead of the YouTube app in your device.
Open your mobile web browser and search YouTube.com for the video you want or paste the link for the video.
Click on the gear icon and make sure that the video has subtitles in your target language. (English in this example).
Avoid using auto-generated subtitles, as they could not be faithful to the audio and incorrect altogether. If auto-generated subtitles are all that's available for your selected video, you can search the web for the correct transcript and then edit your lesson once it is imported.
Click on share -> LingQ
You might need to slide the share options to the left until the "More" button shows (three dots), and then select LingQ.
Choose the target language, edit the Course and level if you wish, and then click Import. When the import is complete, click on "Open" to open the imported lesson on the LingQ app.