Hi Dennis! Assuming you're using one of the VDL templates for Sibelius 5, you'll want to select one of the pre-defined Flexatone instruments setup within the template. You can read more about these in the ReadMe file that comes with the template.
The ";high"; and ";low"; instruments can be treated as pitched instruments, so you can just enter notes chromatically, depending on your needs for the part. The ";Flexatone Bends"; instrument would be treated as unpitched.
Here's a snippet from the Readme that gives the rundown: