How do I identify a software as a medical device under the EU UDI requirements?

Where the software has a physical medium, the UDI shall be placed in human-readable and AIDC formats on every packaging level. 

Where the software has no physical medium, the UDI shall be provided on a readily accessible screen for the user in an easily-readable plain-text format, such as an 'about' file, or included in the start-up screen. Only the human-readable portion of the UDI shall be required in electronic displays of the software (hence not the AIDC format). The physical medium and its packaging containing the software should have the same UDI assigned to the system-level software.  

Softwares lacking a user interface shall be capable of transmitting the UDI through an application programming interface. 

For more details, please see MDR Part C 6.5.4. UDI placement criteria for software: 

https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:02017R0745-20170505&from=EN

And the MDCG guidance on UDI assignment on software as a medical device: https://ec.europa.eu/docsroom/documents/31926