If the board is set to allow for self-join, you should see an option to 'Join Board' at the top of the board (to the right of the board name and visibility settings).
Otherwise, other members can invite you to the board https://help.trello.com/article/717-adding-people-to-a-board
If you had to thrive a new habit during a lockdown, what would it be? Trello
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