Its easy enough to change the fan motor. Access to the fan motor is usually through a removeable panel at the back of the cooker. You will probably need to remove the fan blades, which will probably mean removing the back panel inside the oven which will, in turn mean removing some shelf supports.
Just work safely (Turn the cooker power off) , carefully and methodically and THINK
Use a bit of paper to note where things go and whch way round they are. Don't rely on memory.
A new fan motor is easy enough to get. Check the exact model number of your cooker and look at online suppliers: say espares or ransomes, etc.
If you search YouTube, there may even be the odd video to help
XXX
March 2016