UML Modeling Techniques > Dynamic modeling > State diagram items > Changing an atomic state into a submachine state
  
Changing an atomic state into a submachine state
You can change an Atomic State that owns a State Diagram into a Submachine State that references a State Machine that owns the State Diagram. For example:
To change an atomic state into a submachine state:
Right-click the Atomic State you want to change, and then click Convert to Submachine State.