So you have an aheadset fitted, you've got the'extender' fitted but can't see a way of tensioning the assembly once you've got it all together.
Sounds to me like you've got a quill to ahead adapter and not a steerer tube extender, as if it was an extender, it would have a built in ore-tensioner method like the one pictured above.
Sounds to me like you've got a quill to ahead adapter and not a steerer tube extender, as if it was an extender, it would have a built in ore-tensioner method like the one pictured above.