1/ Via the main dashboard, go to 'Teams'.
2/ On the three dots of the selected team, click on 'Edit team':
3/ Go to the 2nd tab 'Seasonal Teams' and click on the green + button:
4/ Select the new Season for this team, in the dropdown menu of 'Season':
5/ Click "Save and close" The Seasonal team is now added.
General info: user functionalities depend on the roles & permissions settings. If a certain functionality does not work within your user account, this will be because you don't have sufficient permissions for this.