Set environment variable APP_RESTART_CMD="/path/to/your_app_script.sh restart"

Technical assistance
2

it depends on how you installed zammad.

If for example if zammad can be started with systemctl start zammad
You’ll want to look at /etc/systemd/system/zammad.service or if that doesn’t exist /lib/systemd/system/zammad.service

Then see if there’s a line like

EnvironmentFile=-/etc/default/zammad

Then you would put
APP_RESTART_CMD="systemctl restart zammad" # or however you want to restart zammad
in /etc/default/zammad

If that line doesn’t exist you could add the full EnvironmentFile line under [service] and create the /etc/default/zammad file or do whatever other way systemctl has provided to set environment variables.

I haven’t tested any of this, but if systemctl is how you start zammad, then that is where you set the environment variables.