How can I disable editing on forms that have been submitted?

For example, after the customer has completed the form I am able to edit their submission. I NEED this turned off, so I cannot alter the fields.

Hi,

In your Form Settings, there is option to disable Allow Submission Editing.

You can set it to 'Disabled' option to block users editing their submissions.

I hope this help. Let us know if you need further assistance.