There are two run controls in the Optimization module toolbar:

 Run.  This starts the optimization exercise, using the initial guesses.

 Stop.  This stops the optimization exercise.  Pressing run after stop continues the run from the current values.

While running, the value of the parameters and the value of the objective function are updated.  You can stop the optimization exercise at any time, update the model and run in Simulator, to see in more detail how optimization is progressing.