ASND format comes from Adobe Soundbooth a digital audio editor discontinued in 2011, which means that m4a to asnd conversion is something that was mainly done in the past as import of MPEG-4 content to the software for work.
Soundbooth was replaced by Adobe Audition, so perhaps this software might help you out, but otherwise it is unlikely you can produce .asnd files anymore.
In any case, if you have issues with .asnd files, it might be best to reach out to Adobe support or perhaps the online community for further assistance.
Updated: January 5, 2024