The 'CSV Batch Registration' for teams is a feature to modify information of existing teams.
You cannot create new teams from the CSV batch registration screen.
To create new teams, please do so one by one from the 'Team List' and 'Create Team'.
Related:
Manage user teams (Web Browser)
https://teachme.jp/8/manuals/4929282
Update multiple user teams at once using CSV file (Web Browser)
https://teachme.jp/8/manuals/4965352