Part 2 is useless without Part 1. It contains the middle-bulk of the game's data—likely the heavy .BSR (Bethesda Archive) files that hold the high-resolution textures of the tundra and the voice lines of every guard in Whiterun.
If you have Part 1 and Part 2, but the game was actually split into three parts, the "piece" will never be whole. TheElderScrollsVSkyrimSE.part2.rar
To make this "deep piece" whole, you aren't just clicking a button; you are performing a technical synthesis. Part 2 is useless without Part 1