Hi, I'm Daniel welcome to JustAnswer.
Sorry to hear you are having trouble with your washer and sorry for the delay in getting to your question, Lets see if i can help you on this.
To replace the control knob on this you need to do as below.
Unplug the washer.
Then open the door and look on the inside of the door at the top and you will see a cover there held on with a few screws.
Remove all these screws. They are torx screw (star shapped). If you dont have the torx bits then a small flat screwdriver usually works.
Once this cover is off you will see the control board.
Push the wiring block off which is in the bottom left corner and then release the tabs holding the board on and you can remove it from there.
Once you have this off just pull the knob off and you can swap it from there.
Then refit the wiring onto the board and then push it back into place and it will lock itself in place from there.
Try that as you should be able to replace the knob from there.