You cannot open or install "Part 03" on its own. You must have all parts (e.g., Parts 01 through 10) in the same folder for the extraction to work. How to Install from Multi-Part RAR Files
Here is everything you need to know about handling this specific file and completing your installation. What is "Part 03"? The Sims 4 [FitGirl Repack].part03.rar
If you are looking at a file named The Sims 4 [FitGirl Repack].part03.rar , you are likely in the middle of a multi-part download for one of the most popular life-simulation games. Because high-quality game "repacks" are heavily compressed to save you bandwidth, they are often split into smaller "parts" to make downloading easier and more reliable. You cannot open or install "Part 03" on its own
Once you have finished downloading every part of the repack, follow these steps to get the game running: What is "Part 03"