It's OK to just rock forward-backward. Your body and brain are learning the movement.
COGY goes very well with any 4 beat music.
-do you want to build a snowman (from "Frozen")
Not sure how to pedal?
Ask someone to push-pull the chair on a 4 beat music. Here is an example video. After a while, you'll get the feeling and will be able to pedal by yourself.
Use your trunk, rather than just legs.
-swing your body back-forward
-twist your body (at belly button, or pelvis) to left-right
Keep the movement till you have enough momentum to pedal further.
It's OK to keep rocking for ages. Your body and brain are getting used to the movement.
