Vinegar works well. Several years ago I bought a garment steamer, which works very well when it's necessary to help a student whose glue-up needs to be reversed, to help soften wood for bending, and to help remove dents.
If the project allows it, I will use hand screws to slowly and gently ease the joint apart while directing the tip of the steamer's hose at the glue line to soften the glue. I use distilled water to avoid the possibility of discoloring woods, like oak, with a high tanic acid content. Keep your body out of the line of fire - burns from hot water vapor can be painful.
