Select the Holo of the gear in the Outliner and then focus on the Details panel. Under Settings - Initialyou find a dropdown menu with the "1_BP_Part_Mesh" allready in place.
Each time you create a Disassembly of an object using the Transformer, the Part is automatically linked to the Holo via the Init Part and held in place accordingly.
If you break this connection, the Part will not be held in the Holo at the start of the application.
