What do you need to do to fix a problematic convection fan?
The most likely issue is a defective motor. By replacing the motor your convection fan should be working like normal once again. For diagnosis purposes, use a small pointy object to turn the fan blades manually. If there's resistance, the convection fan motor is most likely defective.
Firstly, take the cover off to gain access to the convection fan. After that, the nut keeping the fan in place will need to be taken out. While most screws and nuts come out counter-clockwise, as weird as it is, you might find yourself having to go the opposite way.
Next, take the rear panel off of your oven and gain access to the convection fan motor, typically held in place by a few screws. Connect the new motor in place of the old one. You might need to modify the connector to make it work with the new motor. If you don't have wiring experience, you might want to leave this to an oven repair professional instead.
Usually if the motor won't hook up properly it's because two wires are coupled into a plastic connector that won't connect to the new convection fan motor. By breaking apart the plastic connector you gain gain access to the wires and then connect them to the motor. It's okay for the wires to be unshielded, however you can cover them with electrical tape to be extra precautious.
Turn the oven on and run convection mode when you have your appliance back together. The fan should run like normal once the replacement is done. If not, the problem is due to something else but this is almost never the case for this particular oven repair issue.
Is your electric oven not heating or failing to get hot enough? The most obvious reason would be because of a shorted or damaged heating element. Check if one or both of the elements are failing to work. The bake element (bottom) and broil element (top) can stop functioning due to cracking from food spillovers, other instances of physical damage and even electrical failure. If the elements are not to blame, check that the thermostat and selector switch both work. Also, make sure the temperature-sensing bulb inside of your oven is working properly still.