After installing the ADK on my HDD I decided to install it on my SSD in order to get quicker loading times, however, the Epic Launcher does not want to pick up the existing files and wants to download it all again.
What can I do to get the launcher to recognize these files and not download anything?
I can not help you with your issue but I want to mention that you should be aware that you need a **** big SSD. For reasons I do not want to explain here again you will need ~60gb of space for the ADK and ~60gb of space each time a new patch releases. The patch will not be that big but it will allocate this space before installing. If you wanna know why you can search through the forum since I explained it often enough.
So now you know, so please dont come back next update and ask why you need 60gb of free harddrive space and your SSD is too small. 
I just put my laptop SSD into my desktop so its got 250gb free space so its absolutely fine. I got round to reinstalling it last night and it works now