Use the built-in "Verify Integrity of Game Files" tool in Steam, Epic, or Rockstar Games Launcher. It may take 20 minutes and require downloading 1GB of data, but it is the only guaranteed safe, legal, and effective method.
The naming convention X64a.rpf typically denotes the first significant archive in a series (followed by X64b.rpf , X64c.rpf , etc.), often containing core game assets necessary for the initial boot sequence and open-world streaming. X64a.rpf Download