I gotchu bro.

1. Pick one of the recent images with the dots on top. That'll help. Get the picture up full screen on your phone, as big as it can go.

2. Put the phone about ~1.5ft from your face. Put your thumb halfway between your eyes and the phone.

3. Focus on your thumb and notice that in the backgeound, the out of focus images start to partially overlap.

4. Notice the dots at the top of the image? Try to be aware of them without focusing on them. While keeping your focus on your thumb, move it closer to your face until the dots overlap. You may have to adjust the rotation of your phone a bit.

5. You can then shift your focus from your thumb to the dots. It may take a few trys, but the dots should stay in place. Slowly shift your focus down to the image, and there you go!

Dunno if it'll help but these were the steps that helped my husband do it for the first time:

1. Use a big screen, laptop or monitor, small screens like phones make it more difficult
2. First look at the middle point between both images
3. Now relax your focus to look "through" the screen at a point further in the distance. The two images will go blurry
4. If you're feeling the urge to re-focus on the images, hold it here for a second until you get used to the relaxed focus
5. As your eyes relax more and more, they'll naturally start to cross a bit and you'll see a third "middle" image start to appear. Don't do anything, just keep relaxing that focus and let it happen.
6. At a certain point you're able to sort of snap your focus onto that "middle" image, but it could take a few attempts to correctly judge when to do it without losing all your progress. It's a muscle memory thing, so practise makes perfect.

That may or may not make sense but it's the best way I know to describe it! Good luck.