Hi,
Assuming there are many teams and one "preferred team" (which might change over time), saving is as a user attribute is a good path.
https://www.braze.com/docs/developer_guide/analytics/setting_user_attributes
https://www.braze.com/docs/api/objects_filters/user_attributes_object
You can collect this data using web form, landing page, user profile page, content card, in-app message, as well as email where a click leads to the form / landing page.
As far as which collection point gets the best results, some a/b testing might be in order (I find a combination of channels is best), and of course, Braze intelligent timing (if you have enough send history) can help.
https://www.braze.com/docs/user_guide/brazeai/intelligence/intelligent_channel
