Topic on Talk:ARK: Survival Evolved
Yeah, that same thing happened to me too! I would advise you to move your whole game installation folder to a new location and then open the EpicGames Launcher.
Now check if in your library it shows that you have not installed the game, if not then click install and wait for a few seconds of install then click on the cancel button.
Next, you move the whole Ark game file back to the same location where you just installed the game and let it overwrite the existing game files.
Now open the Epic Games Launcher and now resume the install, instead of downloading the whole game, the launcher will just verify the existed game files which you had downloaded before asking this question on PCGamingWiki. The verification process may take up to half an hour as the game is more than a 100GB in size and when that is done you can simply launch the game like before.