So, let's say you have a fixed camera covering your driveway and a ptz that oversees your entire front area. If the driveway cam is triggered, the ptz would immediately turn to that area and do whatever function you have set in the preset for it.
PTZ Activation Setup - Dahua Wiki This shows a how to on motion detection, Same rules apply for IVS!
So basically, You create an IVS rule and set a tripwire etc. on your fixed camera. Then under the settings for that rule you just created on the fixed camera you can now set a PTZ channel to respond to that tripwire incident. ie. go to preset, tour, scan etc. when that rule or event for your fixed camera is tripped.
Under the IVS rule settings that you set up on the fixed camera you are looking for "PTZ activation" = (settings) this is what you click on to tell what channel ptz to use, preset to go to, activate scan, tour etc.