Seeing as this is an older post and yet the first google result I’ll post here on how I was able to get my new launcher to recognize a pre-existing version of the engine I already had downloaded.
Install the Epic Launcher.
In the default install location, copy your existing version of the engine, however, rename it so that it does not match the typicaly naming convention. In my case, I renamed my existing “4.19” engine directory to “4.19.bkup”
Open the launcher and proceed to download the version of the engine you need. In my case it was 4.19. Once it has started downloading pause the download and close the launcher. Click okay when it prompts you that closing will cancel the download. You should now see the newly created folder and your existing renamed folder.
Delete the newly created engine folder and rename the one you copied back to its original name.
Close the launcher and continue the download on the engine version. The launcher should skip the download portion and simply install and verify the engine.
Once the verification is done the engine should be ready to launch.
