If you want to replace the SK_Mannequin with Adam from the Mixamo Pack so that Adam runs around instead of the silver guy, you do not need to retarget the skeleton. Instead, in the Content Browser, go to: TopDownBP/Blueprints/TopDownCharacter. Open the TopDownCharacter Blueprint, select Mesh (as highlighted below) and in the Details panel change the Skeletal Mesh to “Maximo_Adam” Then in the dropdown menu under “Anim Blueprint Generated Class,” select “MaximoAnimBP_Adam.” Compile and Save.
Now Adam is the character you control:
If this is not the end result you desire, please explain further including why you want to do it that way.
Thanks.