I'm not an expert on this, but I believe that half of the money in your ex's HSA has to be transferred to a new HSA in your name. You first have to open your own HSA. Optum probably has a form for transferring the money, and probably you and your ex both have to sign the form.
You don't have to keep your own HSA with Optum, but they might require you to open an HSA with them in order to do the initial transfer. You could then transfer it to any other trustee that you choose.
Once you open an HSA with Optum, they will, of course, talk to you. But your ex has to initiate the transfer. If you have trouble getting this done, or your ex is uncooperative, ask your divorce lawyer for help.
