As the chair of the committee your responsibilities are similar to what they are during a regular defence, but there are a few details pertaining to digital defences that you should be aware of.
Completely digital defence
During a completely digital defence the procedure is somewhat different from a regular defence, but your responsibilities are similar. Read more about the details here.
Partially digital defence
During a partially digital defence you have additional responsibilities that you need to be aware of as the chair of the committee.