Okay, try this:
Open up any animation asset of yours. Navigate to the Anim Slot Manager window which should be located on the bottom right by default. If it’s not open already, you can open it by navigating to the Window section on the top left and ticking the Anim Slot Manager option under it. Inside the Anim Slot Manager window, click on the Add Slot button and name the new slot. Let’s say we named it “Upper Body”. Then, head back to your anim graph, right click on an empty space and search for “Default Slot” on the menu that pops up. Select the "Slot ‘DefaultSlot’ " option to place the slot node, and click on it. While the node is selected, navigate to the Details window which should be on the top right by default and select the slot named “Upper Body” from the dropdown menu under the Settings section. Plug your red animation node into the Upper Body slot node’s input (Source) pin and plug it’s output pin into the Blend Poses 0 pin of the Layered Blend per Bone node. Then, click on the Layered Blend per Bone node, and while it’s selected, navigate to the Details window and click on the plus (+) button next to the Branch Filters section. (Which should be under Config > Layer Setup) Once that’s done, insert the exact name of the desired bone into the text box next to Bone Name. (The Upper Body slot will only affect those with a lower hierarchy than the bone you choose) You can open up your skeletal mesh asset, decide which bone should the Upper Body start from, copy that bone’s name and paste it into that text box.
Hope this helps! 