I think In general you need to unlink TrackedCam_Unreal _Prev_3-Cam Linked Compound which I think you are using  it like this

Then save it to other folder so it didn't get deleted when you install new aximmetry version

now we can edit this compound by right click and select Edit Compound In-Place

Then we Enter this compound and add what we need for example

Then to add this Pin Collector to input dashboard we right click on it and select Add to control Board

Then we can see the new controller in the INPUTS DashBoard

Finally you need to select  Save in place Modifications to save the changes to this compound

In addition to Ahmed's description: if you want to replace the original keyer with your own one, you first have to find it.
The easiest way is  after entering the "Edit Compound In-Place" mode, go to the control board right-click a KEYER and choose Go To Source Module.

This will take you to the original keyer within the flow graph.

Here you can replace it with your own one, make the connections, and add it to the control board.