What do you mean ? How do you launch the game once you have downloaded it ?
What kind of computer do you have, a Windows, Linux, Mac ?
Try to click on "show local files" on the right panel and double click on "terra nil" executable. I don't know why but the game doesn't want to launch directly in Itch.io but accept to launch from the explorer on my side. (I suspect it launch the "UnityCrashHandler64" instead of "Terra Nil" executable.)