Safety PLC connected to Control PLC

Is the COSY 131 a managed switch?
If so, how can I connect a safety PLC on LAN port 1, to communicate with the control PLC on LAN port 3 to have a secure/reliable communication between them?

The Cosy 131 is not a managed switch. All LAN devices need to be in the same subnet for them to communicate with one another. So if you have a device in port 1 with 192.168.10.45/24 and another device in port 2 with 192.168.10.200/24 they can communicate.

The supplier of the safety PLC says that using a managed switch would eliminate the timeout fault problems I am having. What kind of managed switch could you recommend for COSY?

The LAN side of the Cosy acts as a switch. If the two device are connected though the LAN side of the cosy in the same subnet they can communicate. Not knowing your setup I would not be able to recommend a managed switch. I would try giving are sales team a call since they would be able to help with recommendations on what would work best.