You need all parts (Part 1, Part 2, etc.) in the same folder to extract.
Use WinRAR or 7-Zip to open Part 1, which will automatically pull data from Part 6. Common Issues FrSi_TCRSR.part6.rar
These archives often require a password provided by the original uploader (check the site where you found the links). You need all parts (Part 1, Part 2, etc
If you are missing Part 6, you must download it from the exact same source as the other parts to ensure the checksums match. You need all parts (Part 1