The feature is only available on mobile Metamask apps. It can't be done on Metamask browser extension on other devices. Anyway, right now the mobile sync feature is disabled, so you can't do it either way.
The mobile sync is disabled since a lot of people get deceived by the scammer that make use of that mobile sync.
Yes I know but at least you can synchronized your metamask account on your mobile since the extension can provide qr code to scan for your mobile app metamask rather than manually import your seed phrase. That's also the problem if you are not careful on what you scan as it might be the scammers trap. It's no worry if you scan it from your metamask extension.
I don't know if there is some "hack" to enable the mobile sync feature. But I'm currently running Metamask 10.6.4 and the feature is systematically disabled. So the mobile sync feature is improbable for the default MetaMask settings.
The 'Sync with extension' feature is temporarily disabled.~
Also, as on their FAQ page:
The Mobile Sync feature is currently unavailable. This information will be updated when applicable.