DLR trains have never been designed to be un-staffed. The members of staff on board are called PSAs (Passenger Service Agents) or when the system orginally opened: “Train Captains”.
During normal service they’re responsible for operating the doors, ensuring the train is safe to depart each station and assisting passengers. However they’re also required to drive the trains manually within the depots and also in the event of technical problems with the ATO (Automatic Train Operation) system. DLR trains can’t move under ATO without a PSA using the control panel by the doors.
Its also worth remembering that 8 tube lines are also fitted with ATO (Victoria, Jubilee, Central, Northern, District, Circle, Hammersmith and City, Metropolitan) and the drivers on these lines have a similar role during normal service (except they sit in the cab and they’re officially known as “Train Operators”).
If you’re interested in the role of the PSAs, heres an old training video showing how they’d rescue a failed train, things will have changed since 1988 but its still interesting to see.