You'll probably have to remove the rest of the buttons, the burner and oven knobs and the control panel fascia (Look under the bottom edge and at the back of the top edge for screws. It'll probably swing out form the bottom and slide up to release.
DON'T FORGET TO TURN THE COOKER OFF AT THE MAINS
With the fascia out of the way you may, if you are lucky, be able to grip enough of the button stem to pull it out of the timer body.
If not, then it'll probably mean removing the timer (Making sure you know how to re-set it and switch the oven back tpo Manual when the power goes back on. Note on paper which wires go where on the back) and then CAREFULLY disassembling it enough to push the stems out
Take the opportunity to give all the button stems and the holes in the timer case a clean (Isopropyl alcohol is good - tape head cleaner, etc, or even a small amount of WD40 on a bit of cloth for the button stems and a cotton bud for the holes in the timer body).
Go slowly, carefully and THINK at each step.
Reassemble and go.
XXX, April 2016
