captive nut broke on seat frame bolt?

i have a 1990 toyota mr2 (sw20 chassis) the problem i have is that i removed the seats to clean carpet, upon replacing seats, the rear bolt nearest the door that holds the seat to the chassis has broke its captive nut.

now i cant tighten the bolt up, nor can i remove the bolt or seat as the captive nut is just spinning with the bolt.

do you have any idea how i am able to solve this problem