> The most obvious approach would be to log into their account (from overseas), and transfer the money out.

Yes, this is indeed the most obvious way, but most banks would flag that transfer (especially since it is a large amount) because it was done outside the US.

> But seems like you're wanting something else done instead... so what's the something else?

Optimally you would do that before moving, but I'm assuming that this is beyond their control due to COVID-19 so this is understandable.

Probably very unpopular here (downvote away if you prefer) but this by manually contacting Goldman-Sachs by mail and essentially inform them your particular circumstances. This is understandably a long and frustrating process, but short of physically coming back to the US to sort this then this is the closest method possible.