You have 2 screws holding the manifold to the adapter and then diverted valve.
The screws will either round off or shear off, if they only round off you can remove the diverted and manifold and get some grips or pliers on them. Or you can wiggle the diverted out and then grease up and push new one in without undoing the screws and then when you put it back wedge it in with a bit of copper between the phex and the combustion chamber lol. I have seen that a few times on the HA I used to work for.
They are a pain in the bum to do and I have done loads. Make sure you get a regin diverted valve fibre washer pack.