yea i was thinking that those videos had the other retargeting in it but i guess it was another video somewhere . anyways i linked the docs on retargeting below for your case you want to look at the retargeting adjustments section.
oh and to show the retargeting options you may need to click all bones, active sockets, then show retarget options.
https://docs.unrealengine.com/en-us/Engine/Animation/RetargetingDifferentSkeletons