how can i release the rear seat to lower it

Was it a little cloth teather strap?

yes

To release it you can use needle nose pliers or vise grip needle nose pliers.You would grab where the cloth strap once was.If you wanted to fix it I have a idea to fix it so it wont break again.

ok i will try that,but what do i pull on?

You will have to look into the seat and see where the loop attached it should be a arm in there.Possible with part of a ring that attached the loop to the arm.