If you didn't manually invite Sembly, you probably connected your calendar to Sembly during registration. You can disconnect your calendar in settings to stop Sembly from joining. Follow this link to access calendar settings. Click the three dots next to the calendar you have connected, and select Disconnect. Your meetings will disappear from your meetings list for 2-3 minutes.
If you still have future meetings on your list, check whether you invited Sembly to them using another method. Go to your calendar and check the attendees list.
If you have other members in your workspace, Sembly may have been invited to this meeting by someone else.
You can also toggle off the Attend toggle in the meeting slot to cancel the invite.
