Revise an Estimate
Revising creates a new draft from an estimate you have already sent. You would use it when the customer asks for changes, when the scope shifts after a site visit, or when you want to re-propose after the customer declined. It can be done on an estimate that is awaiting the customer's decision, or one that has been approved or declined.
On the estimate, choose Create Revision, tick the confirmation and choose Create Revision again. The new draft copies the original's details and opens on the edit page. The new revision carries a higher revision number, so everyone can see how the quote evolved, and the earlier estimate is kept as history. Because the revision starts as a draft, you can edit it freely and then send it as its own estimate.
Revisions are how you change an estimate after it has been sent, since sent estimates cannot be edited in place.