If you have a recipe that was developed for TM 21 and you wish to use it in your TM 31 (or vice versa) then the attached files may help  
Thank you, Thermomixer!!!  I printed out the page "Converting Recipe for Use in TM31 or TM21"
I would expect that everyone could use a copy of that.  I see there's an easy solution to the lack of Reverse mode on TM21.  The chart explains how to "use your Butterfly + speed 1 to achieve the same result."
Great information.  And Thermomixer, thanks to for your moderator role in the forum.