You need to assign your skeletal mesh the same skeleton asset that is used by the mannequin. This works if you have made sure to use the same hierarchy and bone naming convention as the mannequin. If you did not use the same skeleton hierarchy then you will have to use re-targeting tools between the two skeletons. If they are the same you will still need to use re-targeting tools to get the animations to look correct on your own model.
https://docs.unrealengine.com/latest/INT/Engine/Animation/RetargetingDifferentSkeletons/
Skeleton Assets: Importing, Sharing Skeletons & Anims | 02 | v4.8 Tutorial Series | Unreal Engine - YouTube “Skeleton Assets: Importing, Sharing Skeletons & Anims | 02 | v4.8 Tutorial Series | Unreal Engine”