To manually sync the Quote/Proposal click the Synchronize with Opportunity button on the Quote Details page, which is visible on a Quote/Proposal that is marked as Primary.
To automatically synchronize Primary Quotes, enable the Auto Sync with Opportunity setting in Proposal System Properties custom setting. This setting syncs Quote/Proposals that are marked as Primary each time the shopping cart is Finalized. CPQ syncs the Quote/Proposal with opportunity again each time you click Accept Quote when Auto Sync with Opportunity is enabled.