the “bad” new: if you are using the FPS template in the engine then it only really has arms, and a gun. you would need to do some steps to replace it with the full mannequin, and for those specific animations you would need to setup animation layers as they do not have data for the torso, head, and legs.
the “good” news is that animations are not that complex to obtain. more recent engine version have a large number of animation in readily available
-through the Animation Blending tutorial from Epic.
-there is Mixamo.com as a source for free animations (and they technically only request attribution not require it, but you might have to do some conversions to retarget the animations)
-and on Fab there are free and low cost animation packs, where things list there for Unreal are strongly encouraged to support the default unreal Mannequin (either Manny or Quin if not both) and/or Meta-humans.