Retargeting animation with new bones

I have some animations from fab which are based on SK_Mannequin skeleton, but it has additional bones in it. For example, R_HandSword

And I have my character which is also based on SK_Mannequin, but it doesn’t have those bones. I manually added R_HandSword to it with unreal skeletal mesh editing tools to the same parent bone.

However, when I try to retarget animations, the R_HandSword bone on my character isn’t being animated.

How can I fix this?

Are you using IK Retargeter, and have you added these bones to the bone chain and set up the mappings?