How do you change viewer option in Optics

from your YouTube tutorial on this instruction video. @ 1:50 where it says to render this out as an animation, select the particle illusion button to launch the interface then you can play the animation in the timeline, the image of the coffee cup and the smoke layer seem to be exported together. Nowhere does it say to make a flattered copy etc……I have done exactly the same thing but when selecting the particle illusion button it just takes the top layer of the animation……. Where do i make the flattened copy? In Optics or PHotoshop? This is confusing! Thanks!
your reply to this was:
" If you’re only seeing the particles in Particle Illusion and not the background, then you probably just need to change the viewer option. Above the viewer there is a button with a little red play button on it. Press that and choose Composite Over Source. Then you’ll see the layer you applied Optics too. Sorry for the confusion."
now maybe I’m being dumb here but I’ve searched and searched thru every place and your user guide to find a button about the viewer with a little red play button on it and can’t find it anywhere. can you be more specific please!! thank you

Hi, you need 2022.5 for it to show in Particle Illusion the effects added in Optics,
earlier versions of Optics only showed the orig image imported in when opening Particle Illlusion,
The View button is at the top of the preview screen

I have 2022.5 and thank you, that’s what I was looking for, I found it. really appreciate your help. it isn’t clear on the YouTube video.!