Try heating the epoxy with with heat gun (work carefully and wear gloves). You may be able to soften the epoxy enough to reposition it . . . if the tail doesn't catch fire first.

If that doesn't work, and depending on the model, you can saw it loose with a hacksaw blade or as fine an X-acto saw or razor saw as you can fit in there and re-attach. The balsa will break long before the epoxy if you try to force it apart. Epoxy is kind of overkill for most joins on a model. Now you see why.