First, check to see how old oven is because some parts may be under warranty and can be fixed for free. You could also check in the stove's manual or call the store where the oven was bought and see what steps to take for repairs.
Remove any tinfoil or other materials from inside the oven. Test the temperature of the oven by placing a thermometer in the middle of the oven to confirm a problem. If there is still a problem you'll need to contact a technician.