after you done rigging your model you

click on the bones and go to edit mode. then again click on one of the bones you want and extrude another bone

like this
also rename with(F2). we need it later



press ALT+P and select clear parent


select the one bone below or above and go to bone constraint properties.


select inverse kinematics from options.

set the target to the main armature

choose the ik bone we made for bone section


you are done
now if you move the IK bone you see that other bones are moving with it

you need ik bones later for example for arms or torso or even head