Re-targeting the rig with mannequin

Hi everyone ,
I am newly join UE 4.27 for game . I have a problem with the character bone re-target in UE with mannequin rig , Both the hand’s finger bone are weirdly attached with the Character. The fbx rig is ok but after re-targeting the rig with mannequin it’s getting distorted .
UE
I have attached the screenshot.
please anyone can help me out thanks.

From my experience, most of the issues are caused by base pose.
Try to adjust the base pose as fit as possible before retargeting.