OK. The first step is to determine which 24v port your pump is connected to. The EB832 has two 24v ports. If you look at the System View in Fusion, it will show all your attached modules. Click your EB832 module to expand it, which will then display each of the eight 120v outputs, and the two 24v DC outputs. The two 24v ports will be the first two white nodes at the bottom below the red ones (those are the 120v AT outputs). These can each be renamed, and you should rename the one where you plugged in the pump so you can easily identify it as the ATO pump. The way to tell which one is which is to manually turn them ON and OFF from your dashboard sliders to see which one turns on the pump.
Next, you need to figure out which of the 6 switch inputs on the Apex is used by the Avast connector. I would assume it's switch 1, but this needs to be confirmed. The best way to do this is to configure the programming on the 24v pump output to turn on if a switch is closed:
Set OFF
If Sw1 CLOSED Then ON
If the pressure switch is under water, then it will report OPEN. If the water is low, it will report CLOSED. Enter this programming on the 24v output, and remove the pressure switch from the water, forcing it to report CLOSED. if the pump turns on, you know you have the correct switch. If it doesn't, then change the programming to:
Set OFF
If Sw2 CLOSED Then ON
Repeat this process with Sw3, Sw4, Sw5, Sw6 until you find the one that turns the pump on.