L.L. Bean Pima cotton button up cardigan top.Mint green. Sz:XL Soft. Long sleeve

L.L. Bean Pima cotton button up cardigan top.Mint green. Sz: XL Soft. Comfortable. Long sleeve. Previously owned but excellent condition. A button is missing. But the spare is on the interior. I just do not know how to sew and would hate to mess up. No rips, stains or defect. Please see pictures for measurements.