Original: However, following the overthrow of the Indonesian regime led by President Sukarno, in a telegram dated 19 September 1966, Indonesia notified the Secretary-General of its decision "to resume full cooperation with the United Nations and to resume participation in its activities starting with the twenty-first session of the General Assembly".
Simplified: On 19 September 1966, decided "to resume full cooperation with the United Nations and to resume participation (start joining) in its activities".