Another Purchase order Question

Another Purchase order Question

when I wish to raise a PO for a software item, I only seem to be able to add sofwtare items that the system already knows about.  THe software item list seems to be populated by virtue of sofwtare that SDP knows about when I have scanned devices.  
 
If I am buying a pirce of software for the first time, it will not have been instaleld, SDP doesnt know about it so its not in my known software ist. How can i manually enter a new sofwtare item into my PO.
 
Thanks

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