Trello – see in Trello who visited or viewed board in the organisation

The way I found to do this, is by changing the Board permissions so that only members can make changes to the Board. People in the Organization can view the board, but they can't become members unless invited to the board.

This way I can invite people to the Organization, let them view the board, and still, they will not be authorized to change anything on the board, and can't join the board without my specific action.

If you still maintain an e-mail account for this user you might temporarily re-enable it with a new password and then use that e-mail address with the "Forgot Password" login process with Trello. A change password e-mail should be sent. (You may need to know the username which should be in the original "Welcome to Trello" e-mail)

Once logged in to Trello as that member (you only removed the member from your organization, not from Trello) you can then add administrators of your choice to the existing boards you wish to transfer. You can also remove any boards no longer needed.

If you are not able to use the e-mail account or otherwise not able to log into the Trello account for that user, I suggest contacting support@trello.com