this should probably be in the OP, instead of just the video showing you how to combine them.You downloaded all 3 parts yes?
then just make a new folder and copy and paste (Ctrl+c/Ctrl+v) each file part1, part2 and part3 into this new folder then open 7zip and use the nav bar at the top of the program to go to the location of your folder you made (you can click in your nav bar in folder copy the location then just paste that in the nav bar in 7zip and hit enter to save time navigating once you can see the 3 files in the folder you made inside of 7zip right click then extract as the video at the bottom of the OP explains