You could try changing the element or the regulator, but to do that you must first know what is causing the problem, and then you need to know the exact name and number of the part that needs to be replaced. An alternative is to get a whole new ring provided again you know the exact name and number that you need. You can replace this yourself, for example there are video instructions here - and you should also be given instructions for your particular model when you get the new part.
However, it may be worth contacting your supplier first to see what they would charge to repair the ring (I'm assuming the cooker is no longer under guarantee). If it isn't too expensive this may be the simplest way.
But if you do want to replace a specific part of the ring you could try following the advice given here.