From chapter 12 of the ePO 4.6 product guide (strongly advise you download a copy too)
Moving systems manually within the System Tree
Use this task to move systems from one group to another in the System Tree. You can move systems from any page that displays a table of systems, including the results of a query.
In addition to the steps below, you can also drag-and-drop systems from the Systems table to any group in the System Tree.
Even if you have a perfectly organized System Tree that mirrors your network hierarchy, and use automated tasks and tools to regularly synchronize your System Tree, you may need to move systems manually between groups. For example, you may need to periodically move systems from the Lost&Found group.
For option definitions, click ? in the interface.
1 Click Menu | Systems | System Tree | Systems and then browse to and select the systems.
2 Click Actions | Directory Management | Move Systems. The Select New Group page appears.
3 Select whether to enable or disable System Tree sorting on the selected systems when they are moved.
4 Select the group in which to place the systems, then click OK.