CS GO command change weaponed hand
cl_righthand 1 - Right hand cl_righthand 0 - Left hand
in console
bind "keyname" "cl_righthand 1" <hit enter>
then
bind "keyname" "cl_righthand 0" <hit enter>
Change keyname to whichever key you want to perform that action.
Alternatively you can use
bind KEY "toggle cl_righthand 0 1"
to have the switch on the same button.