这封英文信该怎么写请以China National Import & Export Corp.的名义向G.P.Glove

To:G.P.Glover & Co.
Fm:China National Imp.& Exp.Corp.
Re:Amend L/C under S/C89stx-5491
Dear sir,
We,as your request,will change the package for the goods under S/C89stx-5491.So please extend the shipmt n validity of the L/C under the S/C89stx-4591 to Aug.31,and Sep.15 .and the other terms keep unchanged.
best regds,
XXXXXXXXXX
(有效期延期至8月31日,并将议付日期延期至9月15日
应为：装运期至8月31日,并将交单有效期延期至9月15日)