Here are a couple of 'as installed' photos to make things clearer. Obviously, these pics show my aftermarket hose, NOT the factory original.
Here's the underbonnet pic of my S60, the solenoid and hose is highlighted: removing the engine cover does make it easier to see but you don't actually need to remove the cover to do the job.
Here's a close-up of the vacuum solenoid. The hose to be replaced is the thicker one, arrowed: just pull it gently but firmly off the solenoid.
And here's a pic of the actuator, on the other end of the hose. Again, pull gently but firmly and it will pull off.
Your new 20cm hose just pushes into place.