Claims can only be amended whilst you are working on it and before submission. Make sure you have all the necessary information with you before you start a claim. You can move back and forth through the form prior to submission and most fields will remain editable during this time. The only difference is on the 'Assessments Affected' page.
Assessments Affected section:
If you made a mistake in the Assessments Affected section, once you submit each entry you can now delete the entry and add a replacement one, but only prior to submission.
The delete button is on the far right of the Assessments Affected table - you will need to scroll all the way across to the far right to find it (as below):
You are unable to submit a previously started form.
Once your EC claim/Enquiry has been submitted the only amendments possible are adding more evidence/upload documents or adding a note. See the FAQ "I submitted my EC claim but noticed a mistake - help!" for further advice.