The likes of Dettol, acetone, soapy warm water etc (someone suggested vinegar, but that might be worse smell after-would than the Dettol..)will help remove excess surface glue, very similarly to removing/stripping paint..but.. melted plastic will remain melted plastic.
You probably know from that, that sometimes it removes the glue "joint" as well if the pieces are not too heavily melted together, more effective with superglue of course, but.
Otherwise the bond is literally made of the plastic itself. So separation becomes a surgical operation?
Mainly its acetone to remove excess glue rather than the bond, so choppy choppy. practice your surgical skills at amputation?
Otherwise hair of the dog ? more plastic cement to melt it more?
Or warm it up and melt it apart
