Thanks for the video. I was a bit impatient and just used a small screw-driver, inserting it in the holes in the back. It magically worked, without force.
Once off, I could see the connector and the type of the LiPo and that also led me to the Molex.
One more questions: how do I remove the LiPo? It seems to be glued to the PCB. I don’t want to work with heat. But that is something for the future, I expect the LiPo to last a while (it is rated for 500 charge cycles).