Retargeting is only required if there is a difference in naming convention between master set of animations and the targeted skeletal rig and is not required when using the same base assets supplied from the Epic market place.
Since the Epic rig shares the same “matched” animations all that is needed in most cases is to change the reference of the rig targeted by the imported animations and since the animations needs a targeted rig one is usually supplied with the animation set.
I found the easy way is to just delete the referenced rig and when the delete dialogue comes up you just have to target the desired rig that you wish to use in the “replace reference with” on the bottom left and all the animations and blueprint references will be referenced to the replacement.
You can also replace the reference one at a time if you wish but in most cases it referred to as replace and not retarget.