How to have Attribute Change Run variant include many master data in PC?

When creating a process chain, I drag Attribute Change Run process type into the right pane, and I want to have this variant to include multiple master data other than only one, but I find I can only add one master data into this Attribute Change Run variant and there is no button to insert other master data. However I did see one Attribute Change Run variant include many master data on another system, I'd be appreciated if someone let me know on how to do this to insert many master data into this variant!