Deletion of existing components is not supported through the REST API within a Change Order context.

The REST API delete operation functions only for components added within the current Change Order. Existing components from a previous revision are not deleted via the API.
Similarly, a PATCH request on the DisableDateTime attribute returns a success status but does not update the component’s end date, and the GET response returns null.

DELETE operation

URL : /fscmRestApi/resources/11.13.18.05/productChangeOrdersV2/{productChangeOrdersV2UniqID}/child/changeOrderAffectedObject/{changeOrderAffectedObjectUniqID}/child/changeOrderAffectedItemStructure/{changeOrderAffectedItemStructureUniqID}/child/affectedItemStructureComponent/{ComponentSequenceId}

How we can delete existing components through rest api on Change Order context?