You can create a custom column by going into the "project" menu in the top left of gantter, then select the "properties" option to open the project's properties.

Then from here you want to select the columns option where you can type in a column name and select the column type. For you it would probably be a text column. Then hit save. 

Then when you go to view menu and hover over custom columns you should see the name of the column you just made, here you can select it to display the column in your CPM. 

Let me know if this is helpful or if you have any additional questions. 

Kind Regards, Sophia