You could disassemble the internals of the brewing unit. There is a kind of round flat spring in there. It is a flat metal ring with a gap (i.e. no full circle). It has got a wave form around its circumference. If you pull it apart so that the "amplitudes" of the waves become bigger. the pressure to the coffee pods may become somewhat greater.

It may only have little effect though, and maybe only for overcoming pod tolerances.

To my surprise, newer Citiz machines (ca. 2019), do not have this pressure relief valve (APD, automatic priming device) anymore.

Instead there is only one hose connected to the water tank port.

The water goes via volumeter into the pump (as usual). Then from pump, the water goes to the location of the former APD.

There, we do not have the 3-way APD anymore, but a simply L-shaped connector leading directly to the entry of the heater/boiler.

To be more precise about these parts:

Referring to the round opening at the back of the brewing unit (third picture of Step 15)

-> Put the small spring on the black piece and insert them into that opening, with the "head" of the black piece oriented outwards.

-> Then insert the transparent joint into that opening and push it down into the opening as far as possible.

Note that the joint has two different sides:

One side has a cylindrical opening which the water hose will go into.

The other side has kind of spherical opening which will sit on / touch the head of the black piece.

@ericlesage , these parts belong in the water entry port of the brewing unit, i.e. where the water hose connects to.