Dell S3148P switch with OS9 - trunk port setup for SPF+ port 49 and 50

Hi, 

Would anybody be able to point me in the right direction to get the following network configuration working.

one switch S3148P

FortiGate HA cluster of 2 FG120G devices

Need to connect each fortigate with 10 Gbit to Dell switch;

- port 49 dell switch to port x3 on fortigate 1

- port 50 dell switch to port x3 on fortigate 2

I cannot find the instructions for the DELL switch ports 49 and 50 to configure these as trunk ports with VLAN1 (untagged), VLAN 10,11,100 (tagged).

Would anyone know the OS9 command to put these 2 ports in trunk mode with the listed VLAN's?

Thanks