Installing without Downloading an Engine?

Hello

My father needed to reformat my PC and some files were lost, but it saved the engine, but the launcher didn’t.
So, how can i install an engine in the launcher without re-downloading the whole engine (Unreal Engine 4.15)
I have a slow connection and I don’t wanna re-download it.
If you have any solution for this, please tell me

Current Specs:
AMD A6-3600M APU
Radeon 3720G2
8GB RAM
750 HDD (350 Remaining)
Windows 10 Pro

If you have new operaring system, you lost all registry entries from unreal. You should be able to just run engine (if you have correct directx and C++ redist installed). But it may be quite unstable, and you never know if its your code or that crooked install. So for peace of mind i suggest downloading it all. To not waste much bandwith you could wait for next engine release which you want to download anyway. Next time your father starts talking about reformatting all tell him to buy new HDD and do dual boot.