For crossing just focus on your finger and then remove it.

Looking far away may be harder, and afaik it’s near impossible to look “past infinity”, iow pictures must be less wide than the distance between your eyes.

Btw these two methods aren’t equivalent in watching stereograms. If you look at one and see something but it doesn’t really make sense, then it’s probably the opposite chirality.

Personally I hate the crossing method because it makes your eyes feel strange for a while.

how I approached crossing: first practice just crossing your eyes and observing how every object has two images in this case and when you slowly “uncross”, they merge back into one. you can use anything in your surroundings.

then for the stereogram you do the same, observe the out of focus edges of the left and right pictures, then slowly uncross until left and right image occupy the same spot as though they were the same object. now its out of focus, but one (ok, actually three, because there were two, you “doubled” that by crossing, then merged two of them. but ignore the other two and focus on the merged pair)

sometimes you will merge images of the same picture, in this case you are just back at your normal vision, repeat :)

then you try to keep them overlapped and focus the vision, try to “believe” that you are really looking at a single object.