It sounds like you will need to uninstall then reinstall Wordfence. That should fix the errors you are getting.
If you have access to Wordfence Options via the dashboard, you might be able to follow the steps here: https://docs.wordfence.com/en/Migrating_wordfence#Migrate_Wordfence_by_Disabling_and_Resetting_the_Wordfence_Plugin. However it may be best to do the full uninstall manually by following the steps I linked to before.
Let me know how it goes.