How to play aim offset while playing anim montage?

hi there.can someone explain how should I set to use aim offset while playing montages and using IK for left hand placement for different guns? for example reload or shooting (shoulder shaking).
I followed some tutorial but I cant really figure out:
and also How should I set to play a “sniper rifle bolt action reloading” montage only on the right arm? (with aim offset as well)
Thanks a lot!