You cannot manually change the display order of Manuals when a Viewer opens a Folder.
You can adjust the display order when a Viewer sorts Manuals by name.
Please add numbers such as "01, 02, 03" or symbols such as "a. b. c." at the beginning of the Manual Title.
If you want Viewers to read Manuals in a specific order, please consider using the portal page feature or the Training feature.
Related:
Switch the display items and sort order of the Manual list (Web Browser version)
https://teachme.jp/8/manuals/9552194
What is the character priority when sorting Manuals by name?
https://help.teachme.jp/hc/en-us/articles/4416535551897
Tell me about the portal page feature
https://help.teachme.jp/hc/en-us/articles/21838465421593
Tell me about the Training feature
https://help.teachme.jp/hc/en-us/articles/7441713539993