@Ingela where are you seeing the board that you don't want to see it anymore? Because you typically will only see boards that you're a member of, or boards you have visited recently (in your recent boards list... which means it'll go away when it's no longer recent)
You can remove a board by going inside the board, then clicking the "show menu" button:
From this menu, select the close board option :
After closing the Board, you can chose to restore the board or to delete it permanently.
Let me know if it helped or not,
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