The lens element looks as if it presses into the frame from the back side. Center it on the frame, hold the frame very stable, maybe a thin wood or carboard on the front side, and push the lens?
The video shows a basic cam adjustment in action. And this cam adjuster is sitting on top of the rangefinder cam arm. The rangefinder cam arm is what reacts to the lens moving in and out, moving this lens which causes the viewfinder image to move. The cam motion is for centering the lens. It may be related to basic centering or may be related to setting infinity, I don't know.
You'll find rangefinder adjustment is what can be called an iterative process. One change affects previous adjustments, etc. Patience. And thought trying to determine which adjustment seems it should go first.
The Yashica is a nice camera to start on. It is common so I bet there is info out there. It is well-done without being expensive. And if you can get it to work, it has an amazing lens.
Preparing a box and some large bags if you are going to learn camera repair. There will be a few cadavers along the way. Bag them up, put them in the box, and save them for parts.