There are many different tools that can be used to edit various features in ROBOLAB. To cycle through them, you can tap the TAB key or click on Window -> Show Tool Palette to see the toolbar containing the tools.The tool used to edit text (and add comments) is selected in the screen shot below:
Alternatively, here is the tool only used to edit text (not for writing comments):
Note: by selecting the wrench on the upper left corner of this toolbar, the black box should turn a bright green. This activates the automatic tool switcher, which should allow for text editing as needed.