You must have Administrator level privileges, or higher, to create and assign users to a team. Contact the account Owner to request access.
In the Boards admin section, Rindle Administrators and Owners can search and manage all boards, even board they don't own, in their Rindle.
To get to the Boards admin section, go to Admin > Boards:
Manage Members of a Board
To manage members of a board, click Manage Members
From here you can edit the permissions of a board member, make someone else the owner of the board, or remove a member from the board.
You can also add new members to the board
When you add someone to a board, they will then be able to see the board in their Boards list.
For example, if you wanted to make yourself the owner of the board you aren't currently a member of, you would add yourself to the board. Then in Members, make yourself the board owner.