The Supply of Goods and Services Act doesn't apply here. Section 1(1) says that the only contracts concerning goods covered by the Act are those 'under which one person transfers or agrees to transfer to another the property in goods'. A lease doesn't transfer the cooker to you: it gives you exclusive possession of a dwelling containing the cooker. The cooker remains the property of the landlord.
Assuming that your lease is for fewer than seven years, the statutory provision for a landlord's repair obligations is set out in s11 Landlord and Tenant Act 1985. Unfortunately this does not help you: although the landlord is responsible for maintaining the gas and electricity supply equipment, the Act specifically excludes 'appliances for making use of the supply of ... gas or electricity'.
The text of your lease may have specific provisions for the repair and upkeep of the cooker, so you should read it carefully and seek advice if you are unsure.
Most landlords will leave copies of the instruction manuals for installed appliances. You should ask for a copy of the manual if one was not provided and can't be found in the flat.
In practical terms, you should report the fault in writing to the landlord (or managing agent if you have one), saying that you are unable to use the cooker and that it is a potential danger given that you don't understand how it works. At the very least, you should ensure that the condition of the cooker is reflected correctly on your inventory.