I'm looking for advice or tips on removing the steering wheel airbag on our 2007 Alhambra. I've followed all advice available on Youtube videos, tried various screwdrivers, tried a special toolkit for this job, but nothing has worked.

The airbag warning light is stuck on (code N95/00588). This problem occurred a couple of years ago and the garage suggested a new clockspring - they took the steering wheel assembly apart then found the after-market clockspring they had ordered was the wrong model, so re-assembled everything with the old existing clockspring still in place. The warning light had disappeared and stayed off for nearly 2 years, so it seemed a poor connection must have been the problem. We want to check if this is the case again, as all steering wheel controls work fine. However I CANNOT get the airbag to pop off by using a screwdriver in the slot behind the wheel. I have literally spent hours trying to do this simple step that should take seconds. I've tried both sides but neither will work. Took a photo inside the access hole and there is a horizontal line through the middle, but can't see if this is a bar, an indent, or a join. Grateful for any advice.

Not done one myself but the video makes it look easy enough, there are two springs that hold the airbag in place.
You will see a small screwdriver is used to push the spring toward the centre and gently pulling the airbag towards you then repeat for the other side.
So when refitting you just push the airbag unit in evenly the springs will open up then click back into place.

Don't forget to disconnect battery before working on any part of the airbag system.

https://www.bigcarclub.com/ford-galaxy-common-faults-and-problems/galaxy-mk2-removing-the-steering-wheel/msg72/#msg72

Have a look at that, might make visualising it easier!