Import code. no. - delete values

I have currently uploaded Commodity codes that are neede when creating Purchase Order  in Item >Import Tab. There is also an Import Code field (EIPO-COIMP) below and there is just one value uploaded perhaps by accident. Requirement was just to upload Commodity codes, and I Import code no. to leave blank. No the 'list'exists with only one value. How can that be deleted?

Regards