You need an extraction tool like WinRAR , 7-Zip , or the RAR app for Android.
Do you have of this file sequence ready for extraction? How to merge .part files using WinRar MSPR2GB.part02.rar
If the process stops and asks for part03.rar , it means that file is missing from your folder. You must download it to continue. You need an extraction tool like WinRAR ,