Many thanks guys for your help, I'm so glad I found this forum. I have TurboCAD 14 and the reference manual for it but it's not really detailed enough.
Henry, I tried the create edit history option first but from what I can see it only works on original 3D objects you have created and not ones that are copied from the original (unless I am missing something). You see I have a number of bent cylinders in my drawing which are all copied from the original one and repositioned. It is one of the copied ones that I was trying to modify. In the selection info top pane all the cylinders are listed as ACIS solids but there is only one tube bend and that is for the original cylinder. I thought of modifying the original, copying it, and then changing it back, but that would mean having to reposition the copy. Instead I tried your second option which was to slice it, rotate it, and add back, which worked well. John, thanks for your suggestion too, thats looks to be another good option.
Do you know if it is possible to use the selection info palette to edit copied 3D objects?