If you want to remove yeast, chill the Fermzilla down to around 50F. Close the butterfly valve and VERY CAREFULLY, slowly unscrew one of the caps on the side of the collection chamber to release any built up pressure. Then you can unscrew the collection chamber.
I usually have a bowl under the FermZilla to catch any mess.
I would suggest you get a couple of carbonation caps to put on the collection chamber. Then, with a short cobra tap, you can put CO2 into the collection chamber and then exhaust it with the cobra tap. I do that about 10 times to reduce the amount of O2 in the chamber. Then I open the butterfly valve.
I, personally, find the collection chamber and the ability to remove yeast and to dry hop with very little O2 added to be the best part of owning FermZillas.