For instructions on how to change the administrator, please refer to the manual here.
▼Change the Administrator (Web Browser Version)
https://teachme.jp/8/manuals/51167056
There can only be one administrator per Group, and no additional administrators can be added.
Sub-administrators, who have almost the same permissions, can be set without any limit on the number of people.
▼Assign a Sub-administrator (Web Browser)
https://teachme.jp/8/manuals/51249069
Related: The administrator is on leave or has left the company, and the administrator role cannot be handed over. What should I do?https://help.series.teachme.jp/hc/en-us/articles/63062116917273
Reference: Change a User's Role (Web Browser)
https://teachme.jp/8/manuals/51248875