The client just changes their IPS and need to change the default router. This article shows how to change and add router on PA-850.
1. Login to the web interface, for example https://192.168.11.11
2. Go to Network>Virtual Routers.
3. Click on default to open Virtual Router – default.
4. Click on Static Routers and then the router you want to make the change, route out in our example.
5. Type the new default gateway IP address over the current IP address.
Note: to add a new router, click on Add icon in the left bottom. Then follow above steps to add a new router.
6. Click Oks and then commit to save the settings.
Please view this step by step video: