The way the system is built, it requires that one name is selected as the Team Leader or Lead Volunteer. The system simply bases this on who’s been in the leadership (line-manager) role the longest. This cannot be manually changed.
However, even though the system has defaulted to one name, either person is still able to pick up any of the line-manager actions. E.g. they can both do reviews or approve permits (if relevant to the role). Even though some actions will have defaulted to one name, it will be up to the persons sharing the role to agree how to share and split the actions between them