I clone my theme to set child theme. I deleted child theme folders in app/design/frontend/ and app/code//ThemeOptions/fixtures but in admin backend it's not removed. I flush cache , Please let me know how to remove my custom child theme.
You can try this :
mysql -u <user> -p -e "delete from <dbname>.theme where theme_path ='<Vendor>/<theme>' AND area ='frontend' limit 1"