If you deleted the admin user by mistake, you can restore the account either in the database directly by changing the value of "status" in table "user" to "2".
Or you perform the following symfony task in the console:
./symfony fix-admin-status
Please note:
When deleting users they will be set to status "deleted" first. Deleted users are deactivated and not visible in the frontend, but an still be restored via the backend. Only "purging" a user will remove him completely from the database. Restoring is not possible afterwards.
