Customers can request changes to estimates.
They can do this by viewing their estimate via their client portal. Once in their portal, they click Finances>Estimates. They can then see what estimates you have sent them. They can view the estimate by clicking the the document button for the invoice.
To request a change they can click the blue “Request Changes” button, type the changes they wish to make and then click “Send Request“
To view these requested changes, you will go to the Finance Tab>Estimates
You will see the change requests in the column labeled “Changes Requested“
Click on the text to view the request. 
From there you can click the blue pencil button to make changes to the estimate. 