Hello, I'm pretty perplexed about this - how did you switch on night mode if there's no settings option for it? Would love to hear more about which phone you have. Screenshots would also be useful to help us diagnose the issue.
Regardless, there is a way to solve this (though it's something of a blunt instrument): you could uninstall the app and reinstall it. That will wipe any settings. Another method would be to go into your phones settings, select "apps", find Sky Map, then "storage" then "clear data". That'll do the same thing. Although this will work it'd be great if we can solve the actual problem though.
Hope this helps,