If you want / need to disconnect the pigtail, gently press the dimple on the WAGO terminal block with your finger (nail) or a small, blunt object.
Take care not to apply pressure outside of the dimples as this might break the connector! You can apply quite a bit of force if you pointed, but not sharp, tool like the official WAGO operating tool.
Note that the connector clamps down hard on the wires and it might have created some indentations in the wire metal. Due to this, it might require some wiggling of the pre-installed pigtail connector to get it out. Press down, pull and jiggle a bit, let it go and then repeat a few times to get it out.