It’s kind of amazing that 4.26 has been released as a preview at the end of September, and the documentation for the Control Rig is still very outdated…anyway:
So first inside the Control Rig, after you used a lot of Get Control Transform nodes in order to drive the various IK handles, you need to use a Set Transform - Control node, promote the translation and rotation ( I did only translation just to test ) to a variable.
Then inside the AnimBP, right click > Control Rig, and you’ll notice that in the details panel you have a pin that you can check, which in my case is the Head Loc.
Then create a BP, add a Skeletal Mesh ( Mannequin ) and use the AnimBP mentioned above.
Here on Tick, cast to that AnimBP, then set the Head Loc, and use a variable ( or whatever you need ) and expose it.
Drag the BP inside your level, hit play, and select the BP, in the details panel you’ll see that you can control the exposed variable, and if you play with the values, you’ll see the head moving/rotating in realtime
Edit: I made a small video about it