I had the same issue, I ended up updating the headset and then resetting by going to Settings > Advanced > Reset Device
Once that is done you might want to plug and unplug (from headset and PC) your link cable if you don't get the prompt.
Once I did this I was able to get the transfer prompt to work. I currently have 10 Vive Focus 3's that I am setting up and I have to do this in order to see in windows explorer.
Hope this helps