​@Anastasia Ignatova - The only way to be added back to the team is for a Team Admin to add you back.

I recently replied to another post with steps on how a team owner/admin can add users to a Free Plan team:

https://community.miro.com/ask-the-community-45/how-to-grant-editing-access-to-other-users-on-the-free-plan-20050?postid=74111#post74111

Or how can I delete them?

Since you are no longer a member of the team, you cannot delete any boards in that team.

Thank you a lot! Hope they will permit my apply… 

All the best!