I would assume you are referring to boards on the "Recently Viewed" area. If that is the case, you can go to Boards (on the top left corner, right besides the Home button).
A list will open with your Starred boards (if you have any) and then the list of Recent Boards. On that list you will see an "X" on the right of the Board's name. Clicking the "X" will remove the Board from your home page.
Hello Community! My name is Brittany Joiner and I am a Trello enthusiast and Atlassian Community Leader. I'll be sharing with you a series of videos with my top tips on how to best use Trello...
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