Once you delete a board on Trello, there’s no way to reverse it. This is why Trello doesn’t have a delete option (at least not a direct one) for boards, cards, and lists.
If you want to delete a board, you have two methods available.
What You Need to Know Before Deleting a Trello Board
Before you try to delete a board, here’s what you should know:
- You cannot delete a board if you’re not the admin for that board. You must request access or ask the admin to delete it.
- You cannot delete a board using the phone app. You must do it from the web version or the desktop application.
- You need to close a board before deleting it. Closed boards can be reopened. However, you can’t recover a board once you’ve deleted it.
Delete a Trello Board From Within the Board
Once you’ve launched Trello on Windows:
- Select Boards from the list of workspaces at the top-left and select the board you want to delete.
- Tap on the Show menu button on the top-right of the Trello board.
Click on the Show menu button from the Trello board you want to delete. - Click More.
Click on More under the Show menu section. - Find Close board in the menu, and confirm by selecting Close.
Click on Close board. 
Click on the red Close button to confirm closing the board. - Next, select Permanently delete board (or Reopen board if you want to continue using it).
You can either select Permanently delete board or Reopen board.
Launch Trello on Windows and:
- Click on Boards. Then, click the View closed boards button at the end to see a list of closed boards.
Click on View closed boards. - The closed boards have two options Delete and Reopen.
You will see a list of closed Trello boards here. - Click on the Delete button to permanently delete a board.
Delete the board from the list of closed boards.