There is no relation with your anim bp. In one blueprint you set an event begin overlap and use the other actor output to check what is the other blueprint with a cast to. Then you set your variable. If you did event in character, variable is there then you set it. If you did it in the other actor, you drag variable from the cast to output and set it. Then your variable is changed. You can see if it works by using a print string on both events begin and end) if it works but not update your anim then trouble is in your anim.
Edit : overlap have to be done with the actor bp, not the anim one so yes you then have to set variable in anim too from character.