The simplest way is to insert homology groups is creating a pseudo atom with the homology group name using the Atom Label Editor tool.
Alternatively, homology groups can be inserted from the Periodic Table's Advanced tab.
Open the Periodic Table (toolbar or from the Atom menu), choose the Advanced tab.
In the Special nodes section, choose the homology group from the dropdown list.
Select the homology group and right-click. Choose Edit Properties... Set the group properties in the dialog box.
Here is an example of the property dialog window for a cycloalkyl group:
By default, the atom and homology group properties are not shown. You can switch it on by checking the View > Advanced > Atom Properties menu.