Personal board will become public

Hi, I’m on free plan, but some time ago Miro gave me an extra personal board as a gift. I don’t really need it, but I cannot delete it, there’s no such button. A couple of days ago I received a notification that this board will become public in a few days and then one of my other booards, which I do need, will become inactive. What can I do to prevent it? Will I be able to delete the private board when it becomes public? Thank you in advance!