(NOTE: this will also clear the current schedule of the light. Unfortunately, there is no way to avoid this):
1.) Make sure your computer is connected to the same network as your light(s).
2.) Launch helioCONNECT. Click scan and select your light(s).
3.) In the top toolbar, click System and then Reboot -> Safe. Your fixture(s) should now restart with default settings (i.e. no password or schedule).
4.) Reconfigure your fixture(s).
How to do a safe reboot of a fixture through helioCONNECT.