The arm is in the photo, just light, so hard to see.It looks like you’re missing a part. The silver post in your photo should have a black polymer arm attached. Here’s a picture of mine:
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The silver post rotates and turns the black arm, which pushes the turning tray. You can set it to rotate the eggs up to eight times per day. The black arm is attached by a tiny cotter pin. You should have gotten these parts in your box. If you didn’t, you need to call them. They are very helpful, in my experience.
I’ve used this incubator several times, and honestly like my foam better. I only use this one because it cost so much, and because it’s easy to see the eggs hatching. Especially important when Duckling is wetting herself trying to see in.

The exposed part of the red wire is making me think it came loose. It was rotating eggs back in... January I think. I just have not been watching much. I have two more hours to wait. Then I will know if it’s rotating or not.