Skeletons won't retarget

High, so I’m new to using unreal and I was watching a tutorial and it got to retargeting the skeleton in the anim starter pack. Unfortunately, it doesn’t seem to be working for some reason. I go to skeleton, I click on the “add new retargeting source” button and click “SK_Manaquin”, but nothing happens. And I did make sure that I was on the right skeleton, but idk what the problem is.