Reset returns the simulation to its initial state - only initial steps active and all variable values cleared - and keeps it running.
Using the toolbar (button):
Click Reset Simulation in the Sequence Explorer view title bar.
Using the keyboard:
Press Ctrl+Shift+F5 (or Cmd+Shift+F5 on Mac).
Using the Command Palette:
Press Ctrl+Shift+P (or Cmd+Shift+P on Mac) and run AutomationView: Reset Simulation.