To uninstall a sensor you need to first find the sensor you want to mark as 'uninstalled' in 'Folder view' and move it to the 'Uninstalled folder.'
The best place to see your 'Uninstalled Folder' is from within the 'Root folder' which is also know as the main organization's folder. If you do not see one, you can create one by creating a new folder.
Once your folder is set up and you have removed the sensor from the floor plan, you can select it and move it to the 'Uninstalled Folder.'
Moving uninstalled devices to this folder will remove them from view and they will only be seen in 'Sensor view' as that is where all sensors, installed or uninstalled, can be viewed.