Train connection with slow walker

Where are you starting your journey and where are you ending and what time? There are always alternatives, like taking a later train or a different route.

Edit - I see there are 3 trains every hour from Nuremberg to Ansbach, every 20 minutes on average, so just take your time and get the next train to Ansbach.

Sorry. I read the website wrong. We have 44 minutes in Nuremberg but only 4 minutes in Ansbach to go from platform 2 to 3 and 4 minutes to go from platform 2 to 5 in Steinach.

I see you are going to Rothenburg then.
Track 2 and 3 at Ansbach are on the same platform, so you just have to walk 10 feet across the platform to the waiting train.
At Steinach, you do have to use the undertrack passageway to get from 2 to 5, but the train to Rothenburg will be there waiting for you on track 5. It only does one thing, go back and forth between Steinach and Rothenburg. When you get off the train at Steinach, let the conductor know you might need a little extra time. Almost everyone making the change here is also going to Rothenburg. If they see you going slow, they will hold the train for a couple of minutes since there is a lot of slack in the schedule.

From track 18 to track 2 in four minutes? That sounds tight, even for someone without a knee replacement (though it would probably be doable for a healthy person if the incoming train is on time). Where did you get that connection? 4 minutes would be sufficient if both trains stopped on the same platform. To my knowledge, 4 minutes is also less than the official minimum connecting time.
There are frequent trains to Ansbach, though. If you book a regional train (S-Bahn, RB, RE) between Nuremberg and Ansbach, you can take a later regional train no matter if you missed the connection due to a train delay or any other reason.
EDIT: Replied to your original question before seeing your own reply. I'm leaving the answer here anyway - maybe it helps someone else one day.

In Steinach you will need to descend from track (Gleis) 2 to an underground passageway, which you use to reach #5, then ascend to that platform. See map of station, with passage in orange:

https://www.stationsdatenbank.bayern-takt.de/StationsdatenbankBEG/station_public_print.html;jsessionid=D2519F0ACF5E728BF5803E0CE994C407?lang=en&efz=8000091

See also Sam's tips.

In Ansbach, all you do is cross the platform from track 2 to 3. See Map below.

https://www.stationsdatenbank.bayern-takt.de/StationsdatenbankBEG/Steckbrief.html?lang=de&efz=8000009

More on the Steinach-Rothenburg train. The train is always scheduled to leave Steinach at 36 past the hour. It takes 14 minutes to get to Rothenburg, arriving at 50 past the hour. It then sits there for 16 minutes, leaving for Steinach at 6 past the hour. Again 14 minute to Steinach, arriving at 20 past the hour and waiting another 16 minutes for its next 36 past the hour departure. So you can see it is under no pressure to leave precisely on time. The rail line has virtually no other traffic on it, maybe a weekly goods train. It is not electrified, the trains are diesel-electric. It is one step up from a bus running on a dedicated road.

Do you have to take your luggage down the stairs at steinbach

Sorry I meant Steinach

The map of the train station at Steinach has a bag at the end of what looks like a conveyer belt but I can’t find a legend of the symbols on the dB site

That is what I have seen at smaller German stations that don't have elevators or escalators. It is a little conveyor belt alongside the stairway you put your luggage on and it moves up to the platform as you walk up alongside it. But don't completely rely on them being operative. Like escalators, they occasionally break down just when you need them the most. But just because you don't see it running, still give it a try. They have sensors that start it as soon as there is a suitcase on it.

That conveyor belt next to the stairway for your luggage while you are going up the stairs is also at Düsseldorf Hbf and also Hannover Hbf.

The map of the train station at Steinach has a bag at the end of what looks like a conveyer belt but I can’t find a legend of the symbols on the dB site

Have youn tried this one? Klick on "Legende" and an explanation of signs will pop up, showing that there are conveyor belts ("Gepäcktransportband"). However, as sam said, don't rely on it too much, some times they are simply not working. There will be enough people around who you can ask for assistance.

and if you put a bag on at the bottom it will go up, and if you put it on at the top it will go down - automagically

The Dutch do a less high tech solution, a narrow ramp. Then you move your bike up or down by muscle power but eliminating the steps for the wheels....

Thanks to everyone for your help