Well, I had the same issue, I had UE4 installed on F drive, then I renamed the drive to D, so installing new launcher produced the same issue.
How I did solve it ?
My installation dir was F:\UE4\EpicGames, the new location was D:\UE4\EpicGames,
So I looked over the registery (regedit.exe) searched for “F:\UE4\EpicGames” and replaced it with “D:\UE4\EpicGames”
You’ll find tons of “F:\UE4\EpicGames”, the correct one in my case was located on
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall
So I suggest you start your search from this directory,
(I have found it exactly under \Uninstall{325AC861-EDAF-440B-97DD-259906E216D3})