The style of the line numbers is specified in Tools > Options > Text Editor > Micro Focus COBOL > Line Numbering, or using the buttons Toggle COBOL line numbering mode and Toggle Standard line numbering mode on the COBOL toolbar.
To remove the COBOL line numbers from source code:
This removes any numbers and text that are in the area for the selected line numbering style.
For example, if you have configured the editor to use COBOL line numbering, unnumbering removes all text from the COBOL sequence area.
You can use Undo to revert the changes.