No need for a cap, it's just a tamper-proof lid. You'll probably need to use tin snips or needlenose pliers to tear the metal down. There's a 10mm nut at the base of the screw that needs to be backed off before you can unscrew it. The metal shield needs to be removed before you can get to that nut.

btw: I'm able to remove my ALDA with the manifold in situ, and others have the reported the same. While it's out, definitely check to see if it can hold 10 psi (pressure) for a sustained period. That should tell you if the seal at the base is functioning properly.