Here is my first attempt at an onigiri press. Since I have not found a model that meets my expectations, I have constructed and tested my own version here.
The handling is very simple and easy to execute.

I put a layer of cling film on the bottom part and then put the wall on it.
Next, a layer of rice is poured in and pressed with the trough punch.
Pour filling of choice into the trough and cover with rice.
The last thing to do is to press everything together with the concave punch. You can push out the finished onigiri with the stamp on the bottom.

Have fun printing and cooking!