replace rubber washer for gas cooker burner

[OM2]

The wife when cleaning the cooker managed to poke out a rubber washer.
See the circle in the image below. The arrow shows something poking out, the washer came from the base of this (she poked it out thinking it was dirt)

Can someone advise where to get from?

It 'looks' like a rubber washer - but has a vertical bit that sticks out.
I searched ebay but can't find. It's a Siemenns gas cooker.

In the picture, I tried unscrewing the bigger circle. Screws come out, but I can't get off the big circle.
I didn't want to force open.
Underneath will reveal where the rubber washer goes.

How do I open this big circle?
Do I need to add anything underneath to reseal after?

Thanks.

 

[gasbanni]

Remove the two screws and the big circle will prise up and off.

There may well be a big fibre washer under the plate that will disintegrate.
Under the hob you will find a data badge that will be needed to order parts.
Post tge image on here ......its not your wife's fault those fibre washe disintegrate. Don't blame her !!!