Yeah, but the “speed” in the blend is just just some kind of value you have given a name of speed, you could have called it orange or anything else for that matter.
So you need to tell the blueprint what value it should get this speed from.
So if its only forward and back movement, then in the event graph of the animation you need to:
Make a “cast to (character class with this animation)”, and as object “get pawn owner”
From the “cast to …” node, you “get velocity” and the “get length” and then “set speed” as this value.
Then you should be good to go, as you now have the speed the character moves with in any direction as a postive value