How do i put 2 animations together?

So i downloaded some animations and it gave me a weird “Fire” animation for the gun then looking at it on a text file showed me it was a additive animation and used another animation “Idle” to work.

I put both of them on UE4 on a AnimBP and tried


PIC: Here is where it should be ( arms on the bottom)
then above is the mesh with this anim bp that was supposed to bring the 2 together (it does it just changes size,location of the mesh for some reason) animation