The Proxy Extract tool is available from the Tools tab, under Clip.
Use the Proxy Extract tool to generate a proxy resolution clip from an existing clip in your project. This is useful when, for example, you have a 4K project, in which you've been working on 2K proxies and want to export a 2K version of your work.
To extract a proxy resolution clip:
You are prompted to pick a Front clip.
You are prompted to pick a render location.
The proxy resolution clip is generated.