hi i am a 79 year old scottish man, i have the same problem.
1- do not concentrate on that mickey mouse red switch because that is not the problem.
2-take some dish soap and a toothbrush on clean all around the rubber gasket.
3-try and pull on where the rubber gasket is all the way round
you will probably see a part of the gasket that wont move at all and thats why it will not open.
put some water in the sink with some dish soap with ,just enough water to cover the gasket
leave in in the sink for about 5 mins. take it out and pull on the sides of the gasket to loosen
the gasket it probably pretty nasty inside keep pullin all the way around the gasket’
once you have done that and got it all loose then push on the red switch on top(mickey mouse)
pushing on the gasket at the same time
4- once you have done all that and it is open. then keep opening & closing it. you will have to
push on the bottom at the same time as you are pressing the red button
on a lighter note once a king always a king once a nifgts enough ha! ha! ha!
we all need a sense of humor at this stage of time. good luck you probably not need good luck