Hi,
It's made on purpose so that you don't delete inadvertedly the data of your custom fields if you don't know what you're doing.
So either:
- you use another column name and you're ok like that
- you use another column name, and once the custom field is created, you can go in your PHPMyAdmin to change the column name of the custom field in the hikashop_field table so that the new custom field will see the data you had previously entered
- you delete the column manually in the target table via your PHPMyadmin and then you can create a custom field with the old column name