Cancel pending or scheduled meetings by navigating to the chat and clicking 'More'.
Find the meeting you would like to cancel from your event schedule, then click on 'Chat' to bring up your conversation. From there, click 'More' in the top right, and then 'Cancel meeting'.
When you cancel meetings, you can leave a message informing your partner why you are cancelling the meeting. This will open the meeting slot up for both of you, so you can either block it or book another meeting.