It's pretty easy, but you'll need RDP access to the SolarWInds server to do this.
Open up Report Writer (green icon that looks like a notepad)
scroll to the Availability subset of reports, and click the report title. A window opens up where you can go to "filter results" tab and from there, add a condition for your machine type. Save your report with a new title ("Availability of Entire Network Last Month - Cisco Only" or similar) and you should be good to go. Report Writer reports can only be modified/copied from the application itself. If this won't work for you, I can see what that report is looking for and recreate one in the Web for you.