The following untested snippet shows the general idea.

// This code snippet will loop through all the pages of the current entry and
// will delete all annotations that are applications of a particular stamp.
// I'm assuming the ID of the stamp is BAD_STAMP_ID.
const int BAD_STAMP_ID = 42;

// this.Entry refers to the entry being processed during this activity. We assume
// it's a document.
ILFDocument doc = (ILFDocument)this.Entry;
doc.LockObject(Lock_Type.LOCK_TYPE_WRITE);
// Retrieve all the object that represents the collection of pages, and obtain
// a listing of all stamp annotations. For each stamp annotation, obtain the
// ILFPage reference that represents the page the annotation is on and then
// look up the annotation object so we can query the stamp ID. If it's equal to
// BAD_STAMP_ID, delete the annotation.
ILFDocumentPages pages = doc.Pages;
ILFAnnotationListing anns = doc.GetAllAnnotations(Annotation_Type.ANN_STAMP);
for (int i = 1, rows = anns.RowCount; i <= rows; i++)
{
    int pageNum = (int)anns.DatumByColType(Annotation_Column.ANNOTATION_COLUMN_PAGE_NUM);
    int itemID = (int)anns.DatumByColType(Annotation_Column.ANNOTATION_COLUMN_ITEM_ID);
    ILFPage page = pages.Item(pageNum);
    ILFStampAnnotation ann = (ILFStampAnnotation)page.GetAnnotationByID(itemID);
    if (ann.StampID == BAD_STAMP_ID)
        page.RemoveAnnotation(ann);
}
// Be sure to unlock when you're done.
doc.Dispose();