During the process of building your Form (beta) block you may want to send some test messages. To delete those test messages afterwards, follow the steps from this article:
- Click on "Developer" in the left vertical menu
- Expand the "Custom Objects"
- Click on block name
- When you hover over the record, you will see an "trash can" icon to delete the record.
You may have to click on the frame of the app simulator to move it out of the way to see this icon.