Students 'on hold'

Hi! All the students I have in the "pending" box are requests that I haven't even gotten a chance to respond to because the message has been unblocked by 5+ teachers. The problem arises that I can't delete them; they stay there all the time. I have also added 2 pictures showing my pending requests and the message I get when the request is accessed.

As a workaround I was wondering if there might be an option to delete these pending messages (old messages), thus leaving room for potential recent messages.

Thank you!