Be very careful with this, wheels can appear to be running backwards at certain speeds because of the frame rates. Check the wheels when the loco is going very slowly. If they are indeed running backwards you will have to edit the loco config.txt file, the tag to be altered in the config is in the bogey section, change "reversed 0" to "reversed 1" or vice versa.
Bill69.
P.S. I am sure you will have seen cars with wheels appearing to run backwards on TV.
Bill69.