What branch of government can propose amendments to the US Constitution that will overturn decisions made by the Supreme Court?

Legislative (the House of Representatives and Senate) can propose Amendments to the Constitution. The Judicial branch's power is to declare laws unconstintutional, so if an amendment is made to the Constitution, then the law is no longer unconstitutional, thus, in a sense, overturning a decision of the Supreme Court.

Congress can also deliberately write laws to circumvent Supreme Court decisions.