Probably the retraction gas cylinders, as they go bad after so many years, operating on their sides. If they are bad, you can push on the extended steering section with your foot to push it back in to locked position, and pin it for safety. If this works easily, then the cylinders are your issue, and a fairly easy fix. If it won't retract without force, then it's likely crud, crap or corrosion in the mechanism (I just had this recently with one of mine). See below for the blinking light fault codes from the TM for clues if it's something else.
The gas cylinders (two) are short lift cylinders (like a hatchback), over the rear-steer section, that push it into locked position when the air cylinder depressurizes. These were originally Guden 40-060-K, but there are many alternative part numbers from many sources, from under $10 to $40 each. If that's your issue, then have a look at @rasmussenrentals video on replacement:
If you can't see the image below, go to the original post here:
https://www.growlerforum.com/forum/garage/four-wheel-steering/122-rear-steering?p=4102#post4102