TC reported "B1" train doors at car 3626did not opened. Staff(CCK) checked and confirmed car 3626 " B1" train doors did not open. Staff (KRJ) later isolatedth e defective train door in closed position. TC reported "B1" ~~~~~ TC reported "B1" train doors at car 3626  did not opened. Staff(CCK) checked and confirmed car 3626 B1" train doors did not open. Staff (KRJ) later isolated  the defective train door in closed position. CE unable to board  Found B1 door LHS outter roller damage. Remove both door and c/o both door into iron black roller. Function test ok. Mating strip/push pull/DLS red line/DSS/Door static and cycle ok. Done by: Koh and Rizman. 03/05/2024.