On a System Architect diagram, you can leave automatic layering on so that System Architect controls layering based on which symbol it determines to be the “containing” symbol, or turn on manual layering by selecting Format > Diagram Format > Symbol Display Layering > User Control. When User Control is turned on, move one symbol on top of another symbol. Right‑click one of the symbols, and choose Symbol Layering, and then select Send to the Front > Send to the Back > Bring Forwards or Send Backwards.