Complex sentence: On 23 March 1969, he replaced Abdul Monem Khan as the governor of East Pakistan but he had to resin from the position a day after upon the declaration of martial law in Pakistan by Yahya Khan.
Split into simpler sentences: On 23 March 1969 he replaced Abdul Monem Khan as the governor of East Pakistan. He was governor for a day which ended upon the declaration of martial law in Pakistan by Yahya Khan.