Don't know if it is too late for this but
The rollover valve slides into two grooves on the top of the tank. Towards the middle and front part of the tank. You can't see the grooves without a mirror or inspection camera. You have to basically put it in by feel. Not fun.

 

I had the same thing happen to me when replacing the in tank pump on a 2015 Tucson 2.0l. I put my phones camera into the hole and was able to see the grooves as described toward the front middle of the tank. I couldn’t get my elbow low enough to put it back into place inside the car though so I had to drop the tank and it was a breeze once I did that. Here’s a pic of what you’re looking for: