Cant align Pose after retargeting

Hey there, im pretty new to unreal engine and explicit to the animating. Ive animated an Character and in my course we now going to attach a Weapon to the Character. All works fin and the retargeting worked like a charm.

BUT! After adding the weapon as a mesh in my player_BP i´ve seen that the weapon is attached at the right bone, but 1. a bit in the wrong direction and the other hand that should be placed at the grip at the front of the weapon is not grabbing it. So i headed in my skeletal mesh and “fixed” the bones while previewing the animation i want it to fix for.

But after saving nothing happens. I know im doing it wrong. Can someone tell me where i can “repose” so the character is holding the weapon like i want it to?

You can go at this in two ways:

a) you can rotate the weapon (usually models have the X axis going the model to towards the front) and see it it aligns ok

b) add a socket to the bone of the hand (set the gun as the preview mesh) and then rotate it accordingly. Then attach the gun to said socket instead of the bone.