Loose wire found in the engine bay

Hi there I'm new here and English is not my first language please be kind . I would like some help about the green wire below any idea what its for how can I fix it. Thanks

Hi

Does anything not work on the engine?

Where does the other end of the wire go to?

The engine work well but has a rough idle when starting but after 2 minutes the idle is normal. I'm just curious about the wire and it bothers me.
This is my first car. I am from south Africa citroen parts here are crazy expensive so I don't want to wait too long for something to happen. Car Mechanics are intimidated to fix this car they advice me to sell as soon as possible but I really love that car. Was a bit extra there but hey...

The wire is coming from that connection

It is not connected to the green wire of the coil pack. It is connected to the shielding of the green wire and is used to "bond" the shield to the engine block.
This can reduce radio frequency "noise" and potential misfires. However it is only used to bond the shield to the same potential as the engine block and doesn't play a part in the engine ignition, which is why the engine is still running.
Good engineering practice would be to terminate the shield at both ends, so you will probably find a shield ground at the connector at the engine ECU. So the shield will still be doing it's thing.
The loose wire should be terminated in a crimp lug under a nut on the coil pack retaining bolt. Unfortunately if care is not taken when removing the coil pack retaining bolt, the lug can be severed from the wire.