Golden Rules of Deleting Contributors from the BEE:
You may not delete anything in a category for which you have no primary data.
Delete estimates for which you've already input a refined value. For example, if you tell the tool you bough 341 kgs of steel chromium 18-8, you would likely want to delete the estimate for Iron and Steel products.
After you've finished refining, use a gut check. Is this something plausibly involved in making your product? Leave it in for good measure. There's no way you aggregated every last thing. Is it something that's definitely not involved? Please feel free to delete it.