how to play off hand

i suggest you mojang   

if  someone play minrcraft on mobile  so he or she  touch left side of mobile screen for use off hand slot   and touch right side for right hand

and if someone play minecraft  on pc  like bluestack,ld player  etc   so he or she use left mouse botton for right hand slots  and right mouse botton for using  off hand slots  and distoy'built use right botton for using