The respondent needs to click the 'Save and edit later' button after submitting the answer. If they miss it, they won't be able to change their answer again, even if they refresh the page.
See Also
How to edit a response in Microsoft Forms | The Jotform BlogForms results only link + Forms version historyForms - saving as you go?Microsoft Forms notifications with shared formClick "Submit" button to submit the response.
In Thank You page, click "Save and edit later" button, form taker will be prompted to sign in.
After sign in, form taker will be redirected to Forms portal and see a Form Card shown under Recent tab.
Click the card, the response form will be opened, and click "Edit response" button to edit and resubmit the response.
