Thank you Mika, my neighbour! I'm Robert the Swede
I've seen some video about removing the plug that way, but the video you sent showed it much better!
I tried to do it a week ago after I watched the video. I tapped lightly and took it slow. It went quite well. The heater fitted well with not much problems.
The difficult part is that it's not much space around there and a little difficult to access.
I had to drain the cooling liquid first also, and refill it afterwards. That part took longest time.
I finished installing the cables few days ago. There's still a few things that needs to be done, like fastening the connector in the front properly.
But it's working as it should!