Hello there! 

Thank you for posting in the Lucidchart Community! Currently there is no way to add another column or delete a column from an ERD shape. But I think that is a great idea! Would you mind adding it to this feature request form? Ideas submitted on this form are directly passed on to our development team for consideration and it would be great to hear your idea. The toolbar listed in documentation like you posted above is the toolbar associated with table shapes. To add a tables to your shape library locate and click on "Shapes" at the top of the left column table and type in "tables" in the search bar. You can then click on the "tables" checkbox and it will show up in your shape library. Once you add one of these table shapes you will have the choice to add/remove rows and columns. You can also change the coloring and merge certain cells to make it look just like the table you posted above. Also with ERD shapes there is an option to insert a table with one two or three columns (see image below).Another workaround would be to insert a UI insert shape. There are certain ones that look just like tables where you can edit how many rows/columns there are. Please let me know if you have any other questions and I would be happy to help!