Proxies

I'm currently working with an editor on a project. I proxied our 4K files down to 720P. I sent the 720P files over to the editor to create the project. They created a new project file instead of using the original one. They have sent me back the project file but I can only view it and export it with the proxied files. There is no option to relink to 4K. Does anyone know how I can re-link my 4K files ?