You may look here:
https://de.wikipedia.org/wiki/Mühlenroute
Sorry, not in english ...
You would have to take the train from Frankfurt then.
Or - you take the train from Frankfurt to Kassel and follow the "Weserradweg" afterwards.
https://www.weser-radweg.de/In the area around the city Münster you will find many good cycling routes.
http://www.muensterland-tourismus.de/We whish you a good tour!