Nazahah
wHAT cAN I dO?
Asalamu Alaikum
I HAVE A PROBLEM AND MY PROBLEM IS I POKE MYSELF IN THE HAND WHEN I'M ANGRY AND I'M GETTING USED TO IT NOW.
wHAT CAN I DO TO STOP THIS?
btw make some dhikr keep the heart moist and recite some Quran daily
wa alaikum as salaam
Angry creeps its ugly head .... dont we all go through this ... but to Poke (hurt urself) well thats of major concern and u shud be treated for this can be pyschological (mental) issues.
Dont get angry this is what the devil wants from u and ur letting him win and on top of that hurting urself 
cool urself down drink some water
make ablution since anger is an ember of fire water will calm it and extinguish it
sit down relax dont talk to move dont think about what makes u anger
dont u love urself enough not to want to hurt urself
Remind urself ukhti ur a creation of God one body is all ur gonna get love it and treat it with respect. Plus think of all the rewards of those who repress their anger.
When angry leave the presence of the people who make you angry..drink water..make wudhu lay down offer salaat,,things like that..Anger always subsides so like give it a few hours till you feel better.
Self harm is sin remember that..Allah watches over you..

Wa 'alaikom Assalam,
It is hard to stop these habits and I know that from experience. Try to stop gradually I guess.