How do i fix error codes 8603

Hi all,
I’m new to selling on Amazon.I’m having problems： You cannot change the ‘item_classification’ for SKU ‘ANG230515497BKS_UKWSDGEN30713-5’ by submitting a feed with a new value. To change this attribute, do the following: 1) Submit a feed to delete the existing SKU. 2) Submit a feed to recreate the SKU with the updated ‘item_classification’.

Can someone please explain to me what to do as I don’t quite understand.

Many thanks