Common issue on most dishwasher distributor matrix.
I do mine every few years (just did it last week in fact). As mine is an older bosh dishwasher the distributor is much bigger, but the principal is the same.
1) The whole assembly should pull up and out. It looks like the top corner is held in place by that corner bracket. Remove the corner bracket, and just pull it up and out from it's o-ring sockets. (finding a youtube video of your model may help, but it should just pull up and out assuming there is nothing else retaining it)
Have a towel down or something to catch the water as there may be remnants in there.
(If your matrix is full of water, one way to trick the dishwasher to empty it is to run a cycle, let the dishwasher drain it as it starts a cycle, then press the reset buttons. This will end the cycle but the dishwasher won't refill it.)
2) Then pull pull out the drain hoses and clamp that clip with some pliers and slide it down the hose then pull off the feed line.
Then...the fun bit..
3) Go to the bathroom (over a bath if you have one) and fill it with a bit of hot water (don't use boiling kettle water) and then get the water to the area you want in the matrix and then shake it (covering any holes you don't want it to leak out of).
Do this a few times and see how much shifts.
4) If nothing much moves, get some milton (or cheap B&M bargins equivalent) and pour it in neat. Again direct it to the area where the fat is and then prop it up somewhere so the milton sits in that area.
It will slowly dissolve the fat. Leave it overnight if needs be.
5) Then go back to the hot water method again, and vigorously shake it so so hot water mashes around in that fatty deposit area.
It will take a bit, but eventually it will all come out.
This method has been tried and tested multiple times by me. I've had ones totally impacted and solid and black. After doing all that they look like brand new.
Edit: additional note, don't forget to keep hold of the o-rings when you remove the matrix. Some may stay in their socket, some may pull out with the matrix.
When you put the matrix back in, put each o-ring back onto the matrix prongs first all the way so they seat against the shoulder. This ensures they are seated nicely when you put the matrix back in.
