Join stage: Link ordering section
The link ordering section on the Stage tab allows you to specify which input link is regarded as the left link and which link is regarded as the right link, and which links are regarded as intermediate.
By default the first link you add is regarded as the left link, and the last one as the right link, with all other links labeled as Intermediate N. You can use this tab to override the default order.
In the example DSLink4 is the left link, click on it to select it then click on the down arrow to convert it into the right link.