Altium Designer: How to select different subcircuits in Schematic and on PCB?
Follow the steps:


Go to View > Workspace Panels > PCB > PCB
Go to PCB Tab.
Here you will see component classes. Here you have the option of selecting components present on the top layer, bottom later etc. You can also choose components from different schematic docs.
Select your sheet (for ex ARC1) and you shall be able to see the number of components on that sheet right below the component classes. 
Select the component from this list and the same shall be highlighted in your PCB.