How can users go back and edit details if the data is encypted?

And I see now that the garbled code is probably because the data is encrypted. But how can users go back and edit details? Surely it shouldn't be encrypted until they submit the form?

The users cannot edit the submissions if the data is encrypted. Only you can do it from the submission page of your form:

How to Edit Submissions Made on Your Forms

If you see the data on the submission page of your form it means that the form was submitted by your user. 

Or do your users maybe see encrypted data on your form? If so, please provide us an ID of your form and if possible a screenshot of the form with encrypted data. 

To find more about encrypted forms, please check this guide:

Encrypted Forms and How to Use Them

I think this is sorted now, thanks.

Sarah