Fortigate 200B help needed to configure GBE Ports as Internal switch

I have a Fortigate 200B.

I have few devices with GBE ports. I want to connect the to GBE Ports 9-12 and setup these ports as part of internal switch FE ports 1-8.

Please tell me if the same is possible, if possible to how to setup the same via CLI / GUI.

Thanks.