Thule 8000 Awning Locks

I'm having trouble tensioning my awning. The motorhome is only 6 weeks old so I'm still leaning a bit about it. There are two braces that run between the front rail (where the legs are) and the arms that run back to the van. They have a tab at the end that appears to be able to switch between locked and unlocked, however neither position seems to do anything? 

Any help or advice would be appreciated.