What you are trying to do is kind of a “cheat” but I’m not above cheating -ha ha. Try this: If you have a project with all three elements, make a copy of the project folder because this may break something. However, I discovered this works: (In your copy project) delete the HeroTPP_Skeleton. It will prompt you to replace the asset at which point you will choose to replace it with the duplicate HeroTPP_Skeleton. Save any referenced files when prompted. Do the same thing for the HeroTPP Skeletal Mesh. As far as the Military Character, you will have to retarget it according the instructions here:
The non-cheating way would be to disregard the default third person altogether then set up custom a Character blueprint and AnimBlueprint for the Anim Starter pack blue man to include all desired animations and be the default controlled pawn set in the level blueprint. (Takes longer, but better in the long run and you will need to learn this eventually.) Then retarget the Military Character to that skeleton. (No getting around that step.)