In the Workflow View, select the Units you want to put into a separate Workflow.
Right-click one of the selected Units and select Create Workflow Unit from selection from the context menu.
You will be asked to provide a name for the new Workflow.
The Units are moved into a separate Workflow and a Workflow Unit is automatically created and placed into the current Workflow. If there were any connections to the respective Units, the Input and Output Ports are automatically created and connected.