Issue the following command to invoke and editor:
[code]svn propedit svn:externals .[/code]

Edit the entries in the file:
[code] http://project.test.xyz/svn/project/abc/trunk abc
http://project.test.xyz/svn/project/cde/trunk cde
[/code]

If not editors are set you won’t be able to edit the file. On UNIX like systems export SVN_EDITOR=vi should do it. On Windows systems, SET SVN_EDITOR=Notepad will set Notepad as the SVN property editor.