You cannot open part06.rar on its own. To extract the game, you must have all parts (e.g., part01 through part10) in the same folder.
If you receive an "Unexpected end of archive" or "Checksum error" during extraction, it usually means part06.rar (or another part) was corrupted during download and needs to be redownloaded. Game Context Fifa.19.part06.rar
Right-click on Part 01 using a tool like WinRAR or 7-Zip and select "Extract Here." The software will automatically pull data from part06.rar and all other parts to recreate the full installation file. You cannot open part06