How can I download the attachment in decodedMessage

In decodedMessage, I got the raw message Data.

How can I get the attachment with this information?

--Apple-Mail=_7074F225-9F70-4410-B0AC-15891A766688
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
	charset=us-ascii
 
Content
--Apple-Mail=_7074F225-9F70-4410-B0AC-15891A766688
Content-Transfer-Encoding: base64
Content-Disposition: ATTACHMENT;
	filename*=utf-8''%E5%8D%97%E4%BA%AC%E5%8D%87%E5%AD%A6%E5%AD%A32021.pptx
Content-Type: application/vnd.openxmlformats-officedocument.presentationml.presentation;
	name="=?utf-8?B?5Y2X5Lqs5Y2H5a2m5a2jMjAyMS5wcHR4?=";
	x-unix-mode=0700
X-Apple-Content-Length: 2299846
 
 
--Apple-Mail=_7074F225-9F70-4410-B0AC-15891A766688--