The information you are looking for is in the CAPAM 3.0.2 documentation under Additional Routes: Additional Routes - CA Privileged Access Manager - 3.0.2 - CA Technologies Documentation
Please review the document, it will supply all the information you need to connect to the other two gateways.
In the screen in Config/Network, click on Additional Routes. When the screen opens up, you will see Add IPV4 Route. Then click on the "?" button at the top left of the popup:
CA Privileged Access Manager - 3.0 : Additional Routes
The information needed is specific to the network you want to reach. This is general networking information that should be available to you. If the information is not available, you would need to speak with your NetOps team for the information needed to complete this form.
This example should help you out:
EX: You have 2 networks: 192.168.1.0 plugged into GB1 & 10.0.0.0 plugged into GB2. The primary network (lets say 192) where your default gateway is, doesn't need a route. You will need to add a route for any other networks. You will need to add a route for the 10 network (with its subnet mask & default gateway, by default the 10 network would be Netmask: 255.0.0.0 & Default Gateway: 10.0.0.1) to go over Device GB2.