How do I get my divorce case dismissed because of Forum Non Conveniens?

you file a motion alleging that. send notice to the other side. argue it. or, better, hire an attorney to do it for you since you do not know how and the attorney should.

Forum Non Conveniens has to be plead within 90 days of the last day you are allowed to answer. It's a creature of caselaw/common law, so it has very peculiar pleading requirements. Best talk to a family law attorney to see what your options are at this stage.

You have not provided enough facts to enable an attorney to answer your question. Depending on how much time has passed, you may have waived your right to raise this issue.