Ctrl + , or Ctrl + Comma or Click portrait on top right and select settings
Change the theme from OS settings to Dark mode.
If your candle colors changed and you do not have a template saved to fix it: go to the web app/browser version of trading view, which should be unchanged, and right click the chart. From there go to color theme and select save as. Close the desktop application and re open it. Then right click on your chart, go to color theme and select the theme you just saved.