Hi,
I guess you mean for creating the product system. I think the manual is quite clear: "he next step is to choose whether to connect to a unit process or a system process if no provider is selected in the process. This setting only has an effect if default providers are not used or not specified, since the default provider is always one specific process, which is then already a unit or system process. " https://greendelta.github.io/openLCA2-manual/prod_sys/Creating.html
Hope this helps