I also can't control my eyes directly, but I can implicitly control them somewhat by deciding what to look at. For parallel viewing, try focusing your eyes on

I also can't control my eyes directly, but I can implicitly control them somewhat by deciding what to look at. For parallel viewing, try focusing your eyes on some object in the distance while still focusing your brain, not your eyes, on the image in front of you. It can take some hours of trying if it is your first time. I find cross-eyed viewing much easier. For cross-eyed viewing, try to focus your eyes on your nose, and then slowly try to focus your brain on the image in front of you, just like when trying look at something in the corner of your eye without side-eying. At the start, this might mean that you see two versions of the image far apart from each other. While focusing your brain on those images, try slowly focusing your eyes a bit more in front of your nose until the images perfectly overlap.