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!