If you want to hire help, try Best Page Forward:
https://www.bestpageforward.net/
Guidance on writing the description yourself:
On Amazon:
https://www.janefriedman.com/amazon-book-descriptions/
General principles:
https://www.publishersweekly.com/pw/by-topic/authors/pw-select/article/78106-how-to-write-better-marketing-copy.html