How to reset alarm bell to louder setting on 930 Deplomat?

I have tried to use the small timer which you can use to time things in the cooker for anything from 1 minute 10 minutes or an hour on my cooker but the bell is set so low I can't hear it when it goes - I do remember several years ago trying to make it louder and there were three settings but for the life of me I can not get the right combination to re-set for loud bell - would be grateful for help.