depending on how much elasticity the internal chord has, you could try to pull it rather taught and tie it off at the top so the inside where the joints are is tight, but this doesn’t always work for a long time. pulling the cable too tight can wear it out much faster.

You can replace the elastic cord in some folding canes. There’s some videos on YouTube that can show you or someone helping you how.

If you're looking for materials, the stretchy cord you might be able to replace with the cord for tent poles, and that might be easier to source. Just an idea.

You could try tying both torn pieces together into a knot.