IIRC, the UN owns the property in Turdle Bay.
The US withdraws from the UN and convinces its allies in the Anglosphere (except the traitorous New Zealanders) to follow. Israel and a handful of G-20 and non G-20 nations would also follow.
Withdraw visas and diplomatic immunity for all UN employees. Serve them notice they are no longer welcome anywhere in the civilized world. The UN would whither and die in two years.