Here is a video showing how to manually operate the convertible top on a BMW Z4, for instance if the hydraulic pump failed. It also shows how to operate the hydraulic release latch in the trunk. This is called the “Bowden cable” whatever that means. Here are the factory instructions, with some notes by me in [ ].

1. In the luggage compartment on the left-hand side below the convertible top compartment floor [TRUNK!], pull out the plastic ring attached to a Bowden cable as far as it will go. [watch video]

2. With a 90-degree turn, lock the plastic handle in this position.
In the hydraulic unit, a short circuit is enabled, making it possible to open and close the folding top by hand.

3. Pull the handle of the Bowden cable in the rear panel of the luggage compartment.
The interlock in the convertible top compartment is released.

4. Move the top forwards by hand until it reaches the cowl panel.

5. Take the Allen key from the on-board toolkit. [as you can see in the video, I didn’t have to use the allen wrench at all]

6. Remove the plastic panel from the front roof brace. [not necessary, generally speaking]

7. Insert the Allen key in the uncovered internal hexagon.

8. Lock and unlock the cowl panel lock by turning the Allen key.

9. Take out and replace the Allen key.

Emergency opening:

1. Perform steps 1 and 2 as well as 5 to 7 from ‘Emergency closing’.

2. Unlock and open the cowl panel lock by turning the Allen key.

3. Take out and replace the Allen key.

4. Move the top backwards until it reaches the convertible top compartment