Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Would you want a total reset, that wipes the programming also? or just enough of a reset to clear the E001 error condition?
Try turning the key to REG (if it isn't there already) and finalize any sales transaction that is still pending (one cause of the E001 error.)
Or, try turning the key to X, then pressing SUBTOTAL, then turn the key back to REG again.
These two remedies can cure the problem. But might be N/A to your machine's problem.
Let me know and I will advise you further. Thanks.