How to delete a design configuration?
Go to your theme table and delete the entry for your created theme, remember the id of the theme from here.
Then go to your
table and search for theme and you will get path records like
replace your default theme id in it.Make sure to flush cache, Reindex.Reference Taken from -
https://magento.stackexchange.com/questions/239392/magento-2-manually-delete-a-design-config-from-my...Credits- Vivek Kumar