You can create new sites under Manage > Topology: Appliances. Select the appliances you want to migrate, and click Migrate Appliances to Sites to display the Site Migration panel.

Select the appliances in the Appliance/Group table to be migrated to single site. Under Option 2, click Create New Site to expand the page and display the controls to create a site. Under Riverbed Appliances, the selected appliances automatically appear. Complete the configuration.