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"
1. login via SSH and execute:
php bin/magento theme:uninstall frontend/your/theme && php bin/magento cache:flush
2. open the database and open the table "theme" and delete the theme entry.
3. execute the following SQL query:
SELECT * FROM `core_config_data` WHERE path LIKE "%theme_id%"
And set the value to "1" to reset to "Magento Base" Theme.
Now you should be able to change your theme in the backend in "Content -> Design -> Configuration"
4. Flush cache again
php bin/magento cache:flush