The Add Attribute is disabled

I am doing Become a Rapid developer course.. Now performing hands On on ‘Add data to your App’.. I am trying to add Attribute in the List View as per mentioned in the course but it seems that the Add Attribute button is disabled for me…. Could any one please help me on the same..  Below is the image attached for reference..
1 answers

Did you set the datasource for the listview?

this should have been done in the previous step of the lecture