How can I fix the programme knob on a Zanussi FL1085?

The exterior knob has come off our Zanussi FL 1085. I've taken off the part beneath that it fitted into and found it has s a bit of plastic broken off. I can't remove any more to get the entire assembly out, though the parts are available on-line, which suggests it's possible to do this. There are two cross headed screws visible but one is so tight that it is impossible to remove - and is there any point in a lay person proceeding any further anyway?