Up ready to fire, should have a pin inserted in hole to prevent accidental firing. In a fire scenario, and the solenoid below that red handle fails to release, you pull pin, and pushdown. It's a manual release, the fact that the solenoid becomes magnetized means it's probably working.
If you don't mind me asking, what is the device connected to? If you found out the solenoid was magnetized, did you disable a tank? If you have exercised that red handle, seems like you won't have to ask this question. I would have thought you might have released something. That seems like an odd place for a control head, are you sure it does anything? Unless that fitting turns back thru the wall, and there is a tank somewhere else, that device is there incorrectly.
The operation of that control head may be the least of your worries. If this is an operational, active , halon system, it would be a good time to do an inspection of the system. I'm talking full functional test to make sure all is in order.
Hope this has helped.