The first way to get a retro-looking photo in Aurora HDR 2018 is to drop the contrast and add some temperature. Then drop the saturation and vibrance as well. This results in a faded and sepia-toned image. Color toning can also aid in creating a vintage look. Tune the highlights and shadows by moving the sliders a little bit to the right. The image will become bright yet yellowish like a washed-out photo. Now go back to the HDR Basic sliders to finish the transformation. Drop the contrast, saturation, and vibrance once again. And here you are with you second variant of the vintage photo.
To learn more tips, check out this video with Jim Nix.