Make two animations affect different bones?

Hello! I was trying to look for tutorials in how to mix 2 different animations at once, but not using a blend space. Like for example: Player1 has a running animation and a attack animation that just makes him swing his right arm. How would I make it so the player WHILE running swings his right arm without affecting any other bones? Let me be a bit more detailed: The attack animation should only affect 3 bones(lets say bone1, bone2, bone3) how is this achieved in unreal engine so only those 3 bones get affected while the rest of them just keep on doing the running animation?