How to assign a skeleton with missing bones?

I have watched this whole line of tutorials. He starts with the adam skeleton and adds the anim starter pack animations, to the adam skeleton.

Im trying to do it the other way.

Ive already set up all of the animation from the anim starter pack, on the top down skeleton. Now I want to retarget the adam skeletal mesh to the top down skeleton. When you click on a skeletal mesh it has an option to assign skeleton. I want my blue guy to be adam, with out changing one animation. Thank you for helping me, im stumped…