From the CLI

create net self 10.46.90.1/24 vlan internal traffic-group traffic-group-local-only allow-service add { tcp:22 }

Check out the self ip address from the CLI to make sure its created

root@(usmifnt01)(cfg-sync In Sync)(Active)(/Common)(tmos)# list net self 10.46.90.1/24 

net self 10.46.90.1/24 { 
	address 10.46.90.1/24 
	allow-service { 
		tcp:22 
	} 
	traffic-group traffic-group-local-only 
	vlan internal 
}

From the GUI

Network - Self IP's - Create

 

I should note that you can not modify the IP Address via CLI or GUI.  You must delete and create the Self IP if you would like to change the IP Address.