I'm not entirely sure I understand what issue you're running into, so forgive me if I'm wrong - it sounds like you can no longer select things on the menu because the Enter key exits the menu? I could've sworn I added in code to prevent that, but it must be an oversight - sorry you ran into that!
If you need to reset your controls, you can do so by venturing to your Local Appdata folder, then the Crisis_Point_2019_Public_Demo folder, and deleting the keys.ini file in there. When you run the game again, it will generate a new keys.ini file with the controls back to default. If you don't know how to do that, hit the Windows key + R keys to open your Run prompt, then in that prompt, type %localappdata% and hit OK. That will open up your AppData/Local folder, at which point you can navigate to the Crisis_Point_2019_Public_Demo folder and remove the aforementioned keys.ini file.
Sorry again you ran into this issue, it'd be best to avoid using the Enter key as a custom keybind for the time being, and I'll make sure the issue is fixed later on. Let me know if that doesn't help or if you need anything else!