So you want to start completely over? I don't have a way 'yet' to start the game over from the main menu.
If you want to start over do this:
Go to %localappdata% in windows folder explorer. Then delete the Sand_Alpha folder you see there.
I hope I understood you correctly :)
No no, lol , I want to play with my base i have made but with the map and missions reset. However, when I start the game with itch.io all my progress is loose I have nothing, I play like a beginner. But I can restart exactly where i was before the update, by pressing "Sand Alpha" in my folder.