The date in the filename ( 29.12.2022 ) suggests this build likely includes the major Together We Rule expansion, which was released in late 2022.
Once you have all parts, simply right-click Part 1 and select "Extract Here." The program will automatically pull data from the subsequent parts (including your Part 4).
Be cautious when downloading .rar files from unofficial sources, as they can contain malware. It is always safer to use official platforms like Steam or the Epic Games Store .