I am a room owner in PHP and occasionally people ask me to delete things. As I understand it, room owners can't and probably never will be able to do that. However, according to http://meta.stackexchange.com/a/87773/170584 I should be able to move messages to another room (such as bin). I have just one question: how? I can't seem to find any way to perform that action. My searches haven't proved helpful as well.
You can click the "room" menu in the top right of the room you're owner of...
...and then select the "move messages" option:
You'll then be able to select the messages you wish to act on and move them to another room using the "relocate" button: