You can use the Prosit library as an iRT calculator directly (when you click Open, you may need to switch the filter on the open file dialog to "*.blib").
Otherwise, if you don't want to use the library and only want to copy values out of it, the library is a SQLite database and you can get the iRT standards from it with a query like:
SELECT PeptideModSeq, Irt FROM IrtLibrary WHERE Standard = 1
Thanks,
Kaipo