How to convert many sketches in to a curve

if you have more than one spline you can use connect curve ,it is in generative shape design as well as also present in sketcher workbench

its already in curve only dude. because sketches also consider as curve only.

IF you to convert, then go to GSD work bench and use EXTRACT command.
You will get as a curve,

İn surface design there is "disassemble" command. it breaks sketch to curves.