Please help me, how can i fix it ???
Ahh, the old twisting mesh problem, it's super easy to fix, just apply the armature pose as the rest pose and it will be fixed
This happens because for some weird reason, when you add IK to a bone it rotates 180 degrees but you wouldn't notice
Before doing this make sure you have all the bones in the rest position or else any pose that you have made will stay like that as the default, a little tip when doing IK: parent the pole target to the ik bonee, so you wont need to be animating it, that just saves you an extra step
just apply the pose as rest pose and that's it :D