according to the Documentation :
When working with Redshift Proxies, it is helpful to follow these guidelines:
You cannot retrieve the original 3d app's (Maya, C4D, Houdini, etc) mesh from a Redshift Proxy file, so it is generally advisable to keep the original source data that was used to export the Redshift Proxy.
image.png
So unless you have the original project file you cannot retrieve the data from the proxy file.