[duns]

I have a Likebook Mars, android 6, new. It was a gift for a friend. I managed to install several apps on it and afterwards it left it off for 2 months or so. Now, re-starting it, it doesn't start: "missing command" and a screen with textual command (restart/apply update fron ADB and so on).
What should i do? I am quite able with Pc (Linux) and I know ADB commans.
Thanks