Is it possible to simplify a 3D looped curve?

I'm trying to reduce a messy set of data into a single curve -to simplify it.

I've tried everything I can think of including Line of Best Fit and Polynomial Regression but can't find a solution that works for complex shapes as pictured below. It's not a simple line/curve. It would be an enclosed shape that potentially passes through itself. To make matters more complex, it's 3D.

The raw data is stored in a List -but it could be converted into something different if that would be beneficial.

Any tips, suggestions, or nudges in the right direction of research would be greatly appreciated!