How can I fix my Worcester 24i boiler?

A dial on the boiler has been pushed inwards and I need to fix it before my parents get back. Its sets when you want the boiler to come on and off. I think its called the programmer? Is it a case of calling someone out or is it safe for me to unscrew the little screws underneath and try pushing it back out? Is it safe to take the bottom bit off? Do you have to disconnect the gas or anything?

Please excuse my lack of knowledge, just don't want to get busted by parents and can do without the ear ache, expensive call out bills etc etc