To remove a Siri Shortcut you created, go to the iotty app and select Automation on the top right, then click on the automation you want to remove:
Once entered in the Siri Shortcut automation, select the trash icon that you find in the top right:
A screen like this will appear, proceed by clicking ok and then select Delete Shortcut:
That's it! You successfully removed the Siri Shortcut automation.