Because The Crew 2's save files are encrypted and tied to your specific Ubisoft account ID, you cannot simply download a random save file and copy it over. It will not work. You need a tool to resign the save file to your account. The community has developed two excellent tools for this:

Extract the downloaded archive (usually a .zip or .rar file). Open the extracted folder to find the save data files.

To prevent the cloud from immediately erasing your new file, you must temporarily disable cloud syncing. Open the desktop client.